diff --git a/classes/completionscanner.php b/classes/completionscanner.php
index 1429d08..fdd4235 100644
--- a/classes/completionscanner.php
+++ b/classes/completionscanner.php
@@ -93,7 +93,7 @@ class completionscanner {
      * @param completion_criteria $crit Criteria to check for
      * @param stdClass $course Course DB record
      */
-    public function __construct(completion_criteria $crit, $course) {
+    public function __construct($crit, $course) {
         $this->courseid = $course->id;
         $this->course = $course;
         $this->modinfo = get_fast_modinfo($course);
diff --git a/classes/coursecompetencyinfo.php b/classes/coursecompetencyinfo.php
index cbb97b2..af20df7 100644
--- a/classes/coursecompetencyinfo.php
+++ b/classes/coursecompetencyinfo.php
@@ -324,6 +324,7 @@ class coursecompetencyinfo {
         $competencies = $this->course_competencies();
         $progress = 0;
 
+
         $cis = [];
         foreach ($competencies as $c) {
             $ci = $this->competencyinfo_model($c, $userid);
@@ -376,6 +377,7 @@ class coursecompetencyinfo {
                     $dcount = 0;
                     $dprogress = 0;
                     $children = [];
+                    $points = 0;
                     foreach ($dids as $did) {
                         $cc = new competency($did);
                         $cci = $this->competencyinfo_model($cc, $userid);
@@ -528,7 +530,7 @@ class coursecompetencyinfo {
      * @param \core_competency\competency $competency
      * @param int $userid
      *
-     * @return stdClass
+     * @return object
      *
      */
     public function proficiency($competency, $userid) {
@@ -559,7 +561,7 @@ class coursecompetencyinfo {
      * @param \core_competency\competency $competency
      * @param int $userid
      *
-     * @return stdClass
+     * @return string
      *
      */
     public function retrievefeedback($competency, $userid) {
@@ -576,7 +578,7 @@ class coursecompetencyinfo {
                 break;
             }
         }
-        return null;
+        return "";
     }
 
     /**
@@ -639,7 +641,7 @@ class coursecompetencyinfo {
                 return boolval($conditions["competencies"][$competency->get("id")]["required"]);
             }
         }
-        return(false);
+        return false;
     }
 
 }
diff --git a/classes/courseinfo.php b/classes/courseinfo.php
index af451ed..6291e46 100644
--- a/classes/courseinfo.php
+++ b/classes/courseinfo.php
@@ -113,7 +113,7 @@ class courseinfo {
 
     /**
      * Check if current user is teacher in this course
-     * @return book
+     * @return bool
      */
     protected function am_teacher(): bool {
         global $USER;
@@ -216,12 +216,12 @@ class courseinfo {
     public function displayname() {
         $displayfield = get_config("local_treestudyplan", "display_field");
         if ($displayfield == "idnumber") {
-            $idnumber = trim(preg_replace("/\s+/u", " ", $this->course->idnumber));
+            $idnumber = trim((string)(preg_replace("/\s+/u", " ", $this->course->idnumber)));
             if (strlen($idnumber) > 0) {
                 return $this->course->idnumber;
             }
         } else if ($displayfield == "fullname") {
-            $fullname = trim(preg_replace("/\s+/u", " ", $this->course->fullname));
+            $fullname = trim((string)(preg_replace("/\s+/u", " ", $this->course->fullname)));
             if (strlen($fullname) > 0) {
                 return $fullname;
             }
@@ -232,7 +232,7 @@ class courseinfo {
             $datas = $handler->get_instance_data($this->course->id);
             foreach ($datas as $data) {
                 if ($data->get_field()->get('shortname') == $fieldname) {
-                    $value = trim(preg_replace("/\s+/u", " ", $data->get_value()));
+                    $value = trim((string)(preg_replace("/\s+/u", " ", $data->get_value())));
                     if (strlen($value) > 0) {
                         return $value;
                     }
@@ -577,7 +577,7 @@ class courseinfo {
             );
             return [$value, "textarea", $this->course()->summary];
         } else if ($fieldname == "idnumber") {
-            $idnumber = trim(preg_replace("/\s+/u", " ", $this->course->idnumber));
+            $idnumber = trim((string)(preg_replace("/\s+/u", " ", $this->course->idnumber)));
             return [$idnumber, "text", $this->course->idnumber];
         } else if ($fieldname == "contacts") {
             $cle = new \core_course_list_element($this->course());
diff --git a/classes/courseservice.php b/classes/courseservice.php
index eec4da5..1fc11f1 100644
--- a/classes/courseservice.php
+++ b/classes/courseservice.php
@@ -117,7 +117,7 @@ class courseservice extends \external_api {
                 if (count($intersect) == 0) {
                     // Double check permissions according to the moodle capability system.
                     $ctx = \context::instance_by_id($r->id);
-                    if (has_capability($capability, $ctx, $userid)) {
+                    if (is_object($ctx) && has_capability($capability, $ctx, $userid)) {
                         // Get the category, and double check if the category is visible to the current user.
                         // Just in case it is a hidden category and the user does not have the viewhidden permission.
                         $cat = \core_course_category::get($r->instanceid, \IGNORE_MISSING, false, $userid);
@@ -184,7 +184,7 @@ class courseservice extends \external_api {
             if (count($intersect) == 0) {
                 // Double check permissions according to the moodle capability system.
                 $ctx = \context::instance_by_id($r->id);
-                if (has_capability($capability, $ctx, $userid)) {
+                if (is_object($ctx) && has_capability($capability, $ctx, $userid)) {
                     // Get the category, and double check if the category is visible to the current user.
                     // Just in case it is a hidden category and the user does not have the viewhidden permission.
                     $cat = \core_course_category::get($r->instanceid, \IGNORE_MISSING, false, $userid);
@@ -265,7 +265,7 @@ class courseservice extends \external_api {
                     $children = self::user_tops();
                 } else if ($context->contextlevel == \CONTEXT_COURSECAT) {
                     $cat = \core_course_category::get($context->instanceid, \MUST_EXIST, true);
-                    if ($cat->is_uservisible()) {
+                    if (is_object($cat) && $cat->is_uservisible()) {
                         $children = [$cat];
                     } else {
                         $ci = new contextinfo($context);
@@ -309,10 +309,13 @@ class courseservice extends \external_api {
     /**
      * Get category info by id
      * @param mixed $id
-     * @return array
+     * @return \core_course_category
      */
     public static function get_category($id) {
         $cat = \core_course_category::get($id);
+        if (!is_object($cat)) {
+            throw new moodle_exception("unknownerror");
+        }
         return static::map_category($cat);
     }
 
@@ -439,7 +442,7 @@ class courseservice extends \external_api {
             $contextcounts[$r->context_id] = $r->num;
             // Add any of the categories containing studyplans to the list.
             $ctx = \context::instance_by_id($r->context_id);
-            if (has_capability($capability, $ctx) && !in_array($r->context_id, $contextids)) {
+            if (is_object($ctx) && has_capability($capability, $ctx) && !in_array($r->context_id, $contextids)) {
                 $insertctxs[] = $ctx;
             }
         }
@@ -454,7 +457,7 @@ class courseservice extends \external_api {
                 // Get the context.
                 $refctx = \context::instance_by_id($refctxid);
                 // Double check permissions.
-                if (has_capability($capability, $refctx)) {
+                if (is_object($refctx) && has_capability($capability, $refctx)) {
                     $insertctxs[] = $refctx;
                 }
             } catch (\dml_missing_record_exception $x) {
@@ -489,19 +492,24 @@ class courseservice extends \external_api {
         foreach ($contextids as $ctxid) {
             try {
                 $ctx = \context::instance_by_id($ctxid);
-                if ($ctx->contextlevel == CONTEXT_SYSTEM) {
+                if (is_object($ctx) && $ctx->contextlevel == CONTEXT_SYSTEM) {
                     $cat = \core_course_category::top();
-                } else if ($ctx->contextlevel == CONTEXT_COURSECAT) {
+                } else if (is_object($ctx) && $ctx->contextlevel == CONTEXT_COURSECAT) {
                     $cat = \core_course_category::get($ctx->instanceid, \MUST_EXIST, false);
+                } else {
+                    $cat = null;
                 }
-                $cats[] = $cat;
-                // In edit mode, also include direct children of the currently selected context.
-                if ($operation == "edit" && $ctxid == $refctxid) {
-                    // Include direct children for navigation purposes.
-                    foreach ($cat->get_children() as $ccat) {
-                        $ccatctx = \context_coursecat::instance($ccat->id);
-                        if (!in_array($ccatctx->id, $contextids)) {
-                            $cats[] = $ccat;
+
+                if ($cat != null) {
+                    $cats[] = $cat;
+                    // In edit mode, also include direct children of the currently selected context.
+                    if ($operation == "edit" && $ctxid == $refctxid) {
+                        // Include direct children for navigation purposes.
+                        foreach ($cat->get_children() as $ccat) {
+                            $ccatctx = \context_coursecat::instance($ccat->id);
+                            if (!in_array($ccatctx->id, $contextids)) {
+                                $cats[] = $ccat;
+                            }
                         }
                     }
                 }
@@ -566,6 +574,10 @@ class courseservice extends \external_api {
         // Retrieve grade item.
         $gi = \grade_item::fetch(["id" => $gradeitemid]);
 
+        if (!is_object($gi)) {
+            throw new moodle_exception("unknownerror");
+        }
+
         // Validate course is linked to studyplan.
         $courseid = $gi->courseid;
         if (!$o->course_linked($courseid)) {
diff --git a/classes/form/formbase.php b/classes/form/formbase.php
index 1ddcca3..3a4e0f7 100644
--- a/classes/form/formbase.php
+++ b/classes/form/formbase.php
@@ -60,7 +60,7 @@ abstract class formbase extends \moodleform {
      * Also validate parameters and access permissions here
      *
      * @param object $customdata The form customdata built on form initialization in self::init_customdata(...)
-     * @return array Form data based on parameters
+     * @return object Form data based on parameters
      */
     abstract public function init_formdata(object $customdata);
 
@@ -79,14 +79,14 @@ abstract class formbase extends \moodleform {
     /**
      * Process the submission and perform necessary actions
      * @param object $entry The processed form data
-     * @return object|array Data to pass to receiver if submission successful
+     * @return mixed Data to pass to receiver if submission successful
      * @throws \moodle_exception if an error must be given for a specific reason.
      */
     abstract protected function process_submitted_data(object $entry);
 
     /**
      * Process the submission and perform necessary actions
-     * @return object|array Data to pass to receiver if submission successful
+     * @return mixed Data to pass to receiver if submission successful
      * @throws \moodle_exception if an error must be given for a specific reason.
      */
     public function process_submission() {
diff --git a/classes/form/studyplan_editform.php b/classes/form/studyplan_editform.php
index 360482d..fdbf511 100644
--- a/classes/form/studyplan_editform.php
+++ b/classes/form/studyplan_editform.php
@@ -50,7 +50,7 @@ class studyplan_editform extends formbase {
      * Translate parameters into customdata.
      *
      * @param object $params The parameters for form initialization
-     * @return stdClass Form data based on parameters
+     * @return object Form data based on parameters
      */
     public static function init_customdata(object $params) {
         $customdata = new stdClass;
@@ -58,7 +58,6 @@ class studyplan_editform extends formbase {
         if ($customdata->create) {
             $customdata->context = \context::instance_by_id($params->contextid);
         } else {
-
             $customdata->plan = studyplan::find_by_id($params->studyplan_id);
             $customdata->context = $customdata->plan->context();
             $customdata->simplemodel = $customdata->plan->simple_model();
@@ -314,7 +313,7 @@ class studyplan_editform extends formbase {
     /**
      * Process the submitted data and perform necessary actions
      * @param object $entry The processed form data;
-     * @return bool false if submission not successful
+     * @return mixed Data to pass to receiver if submission successful
      * @throws \moodle_exception if an error must be given for a specific reason.
      */
     protected function process_submitted_data($entry) {
diff --git a/classes/form/studyplan_fromtemplateform.php b/classes/form/studyplan_fromtemplateform.php
index 7a6ac11..0cc4f80 100644
--- a/classes/form/studyplan_fromtemplateform.php
+++ b/classes/form/studyplan_fromtemplateform.php
@@ -48,7 +48,7 @@ class studyplan_fromtemplateform extends formbase {
      * Translate parameters into customdata.
      *
      * @param object $params The parameters for form initialization
-     * @return array Form data based on parameters
+     * @return object Form data based on parameters
      */
     public static function init_customdata(object $params) {
         $customdata = new stdClass;
@@ -62,7 +62,7 @@ class studyplan_fromtemplateform extends formbase {
      * Also validate parameters and access permissions here
      *
      * @param object $customdata The parameters for form initialization
-     * @return array Form data based on parameters
+     * @return object Form data based on parameters
      */
     public function init_formdata(object $customdata) {
         global $DB;
@@ -166,7 +166,7 @@ class studyplan_fromtemplateform extends formbase {
     /**
      * Process the submitted data and perform necessary actions
      * @param object $entry The processed form data;
-     * @return bool false if submission not successful
+     * @return mixed Data to pass to receiver if submission successful
      * @throws \moodle_exception if an error must be given for a specific reason.
      */
     protected function process_submitted_data($entry) {
diff --git a/classes/form/studyplanpage_editform.php b/classes/form/studyplanpage_editform.php
index 36bebf8..97b7b4b 100644
--- a/classes/form/studyplanpage_editform.php
+++ b/classes/form/studyplanpage_editform.php
@@ -47,7 +47,7 @@ class studyplanpage_editform extends formbase {
      * Translate parameters into customdata.
      *
      * @param object $params The parameters for form initialization
-     * @return array Form data based on parameters
+     * @return object Form data based on parameters
      */
     public static function init_customdata(object $params) {
         $customdata = new stdClass;
@@ -84,7 +84,7 @@ class studyplanpage_editform extends formbase {
      * Also validate parameters and access permissions here
      *
      * @param object $customdata The parameters for form initialization
-     * @return array Form data based on parameters
+     * @return object Form data based on parameters
      */
     public function init_formdata(object $customdata) {
         global $DB;
@@ -199,7 +199,7 @@ class studyplanpage_editform extends formbase {
     /**
      * Process the submitted data and perform necessary actions
      * @param object $entry The processed form data;
-     * @return bool false if submission not successful
+     * @return mixed Data to pass to receiver if submission successful
      * @throws \moodle_exception if an error must be given for a specific reason.
      */
     protected function process_submitted_data($entry) {
diff --git a/classes/form/text_integer.php b/classes/form/text_integer.php
index 0476b4d..dcf540f 100644
--- a/classes/form/text_integer.php
+++ b/classes/form/text_integer.php
@@ -39,7 +39,6 @@ class text_integer extends MoodleQuickForm_text {
      * @param object $renderer An HTML_QuickForm_Renderer object
      * @param bool $required Whether an element is required
      * @param string $error An error message associated with an element
-     * @return void
      */
     public function accept(&$renderer, $required = false, $error = null) {
         global $OUTPUT;
diff --git a/classes/gradeinfo.php b/classes/gradeinfo.php
index 2d8148d..5e15f91 100644
--- a/classes/gradeinfo.php
+++ b/classes/gradeinfo.php
@@ -153,7 +153,7 @@ class gradeinfo {
      */
     public static function get_coursecontext_by_id($id): \context_course {
         $gi = grade_item::fetch(["id" => $id]);
-        if (!$gi || course_module_instance_pending_deletion($gi->courseid, $gi->itemmodule, $gi->iteminstance)) {
+        if (!is_object($gi) || course_module_instance_pending_deletion($gi->courseid, $gi->itemmodule, $gi->iteminstance)) {
             throw new \InvalidArgumentException ("Grade {$id} not found in database");
         }
         return \context_course::instance($gi->courseid);;
@@ -169,7 +169,7 @@ class gradeinfo {
         $this->studyitem = $studyitem;
 
         $gi = grade_item::fetch(["id" => $id]);
-        if (!$gi || course_module_instance_pending_deletion($gi->courseid, $gi->itemmodule, $gi->iteminstance)) {
+        if (!is_object($gi) || course_module_instance_pending_deletion($gi->courseid, $gi->itemmodule, $gi->iteminstance)) {
             throw new \InvalidArgumentException ("Grade {$id} not found in database");
         }
         $this->id = $id;
@@ -248,10 +248,10 @@ class gradeinfo {
             $r = $DB->get_record('local_treestudyplan_gradeinc',
                                  ['studyitem_id' => $this->studyitem->id(), 'grade_item_id' => $this->gradeitem->id]);
             if ($r && $r->include && $r->required) {
-                return(true);
+                return true;
             }
         }
-        return(false);
+        return false;
     }
 
     /**
@@ -339,7 +339,7 @@ class gradeinfo {
      */
     public function user_model($userid) {
         global $DB;
-        $grade = $this->gradeitem->get_final($userid);
+        $grade = (object)$this->gradeitem->get_final($userid);
         // Format grade for proper display.
         if (is_object($grade)) {
             $finalgrade = \grade_format_gradevalue($grade->finalgrade, $this->gradeitem, true, null, 1);
diff --git a/classes/gradingscanner.php b/classes/gradingscanner.php
index ebddd0b..84b7922 100644
--- a/classes/gradingscanner.php
+++ b/classes/gradingscanner.php
@@ -148,7 +148,7 @@ class gradingscanner {
                 // First check if the completion needs grading.
                 $ungraded++;
             } else {
-                $grade = $this->gi->get_final($userid);
+                $grade = (object)($this->gi->get_final($userid));
                 if ((!empty($grade->finalgrade)) && is_numeric($grade->finalgrade)) {
                     // Compare grade to minimum grade.
                     if ($this->grade_passed($grade)) {
diff --git a/classes/local/aggregators/bistate_aggregator.php b/classes/local/aggregators/bistate_aggregator.php
index 973e92d..4a7ffde 100644
--- a/classes/local/aggregators/bistate_aggregator.php
+++ b/classes/local/aggregators/bistate_aggregator.php
@@ -326,7 +326,7 @@ class bistate_aggregator extends \local_treestudyplan\aggregator {
         $course = \get_course($gradeitem->courseid); // Fetch course from cache.
         $coursefinished = ($course->enddate) ? ($course->enddate < time()) : false;
 
-        if (empty($grade)) {
+        if (!is_object($grade) || empty($grade)) {
             return completion::INCOMPLETE;
         } else if ($grade->finalgrade === null) {
             // On assignments, grade NULL means a submission has not yet been graded, .
@@ -341,7 +341,6 @@ class bistate_aggregator extends \local_treestudyplan\aggregator {
                 return completion::INCOMPLETE;
             }
         } else {
-            $grade = $gradeitem->get_final($userid);
             // First determine if we have a grade_config for this scale or this maximum grade.
             $finalgrade = $grade->finalgrade;
             $scale = $gradeinfo->get_scale();
diff --git a/classes/local/aggregators/competency_aggregator.php b/classes/local/aggregators/competency_aggregator.php
index cac36f9..7f95da4 100644
--- a/classes/local/aggregators/competency_aggregator.php
+++ b/classes/local/aggregators/competency_aggregator.php
@@ -289,6 +289,7 @@ class competency_aggregator extends \local_treestudyplan\aggregator {
      */
     public function grade_completion(gradeinfo $gradeinfo, $userid) {
         // COURSE COMPETENCIES DOESN'T REALLY USE THIS FUNCTION.
+        return 0;
     }
 
 }
diff --git a/classes/local/aggregators/core_aggregator.php b/classes/local/aggregators/core_aggregator.php
index fe9c5a3..38900f8 100644
--- a/classes/local/aggregators/core_aggregator.php
+++ b/classes/local/aggregators/core_aggregator.php
@@ -216,6 +216,7 @@ class core_aggregator extends \local_treestudyplan\aggregator {
      */
     public function grade_completion(gradeinfo $gradeinfo, $userid) {
         // CORE COMPLETION DOESN'T REALLY USE THIS FUNCTION.
+        return 0;
     }
 
 }
diff --git a/classes/local/aggregators/tristate_aggregator.php b/classes/local/aggregators/tristate_aggregator.php
index 6c62571..0928e22 100644
--- a/classes/local/aggregators/tristate_aggregator.php
+++ b/classes/local/aggregators/tristate_aggregator.php
@@ -114,7 +114,7 @@ class tristate_aggregator extends \local_treestudyplan\aggregator {
             }
         } else {
             // Indeterminable.
-            return null;
+            return completion::INCOMPLETE;
         }
     }
 
@@ -167,7 +167,7 @@ class tristate_aggregator extends \local_treestudyplan\aggregator {
         $gradeitem = $gradeinfo->get_gradeitem();
         $grade = $gradeitem->get_final($userid);
 
-        if (empty($grade)) {
+        if (!is_object($grade) || empty($grade)) {
             return completion::INCOMPLETE;
         } else if ($grade->finalgrade === null) {
             // On assignments, grade NULL means a submission has not yet been graded, .
diff --git a/classes/local/gradegenerator.php b/classes/local/gradegenerator.php
index 5961157..37587c7 100644
--- a/classes/local/gradegenerator.php
+++ b/classes/local/gradegenerator.php
@@ -214,7 +214,7 @@ class gradegenerator {
      * @param string $student Student identifier
      * @param string $skill Skill identifier
      * @param gradeinfo[] $gradeinfos
-     * @return stdClass[] List of gradeinfo related results ready to add
+     * @return array List of gradeinfo related results ready to add
      */
     public function generate(string $student, string $skill, array $gradeinfos ) {
         global $DB;
@@ -330,9 +330,12 @@ class gradegenerator {
      * Store skills table into a string
      * @return string|null Json encoded string of the skills table
      */
-    public function serialize(): ?string {
-        return json_encode([
-            "table" => $this->table], JSON_PRETTY_PRINT);
+    public function serialize(): string {
+        $s = json_encode(["table" => $this->table], JSON_PRETTY_PRINT);
+        if (!is_string($s)) {
+            return "";
+        }
+        return $s;
     }
 
     /**
diff --git a/classes/local/helpers/webservicehelper.php b/classes/local/helpers/webservicehelper.php
index c43bd3a..e3f5989 100644
--- a/classes/local/helpers/webservicehelper.php
+++ b/classes/local/helpers/webservicehelper.php
@@ -44,7 +44,7 @@ class webservicehelper {
      * @param array|string $capability One or more capabilities to be tested OR wise
      * @param \context $context The context in which to check for the capability.
      * @throws \webservice_access_exception If none of the capabilities provided are given to the current user
-     * @return boolean
+     * @return bool
      */
     public static function has_capabilities($capability, $context) {
 
@@ -55,7 +55,7 @@ class webservicehelper {
         if (is_array($capability)) {
             return \has_any_capability($capability, $context);
         } else {
-            return has_capability($capability, $context);
+            return \has_capability($capability, $context);
         }
     }
 
@@ -63,7 +63,7 @@ class webservicehelper {
      * Test if the current user has a certain capability in any of the categories they have access to
      * @param string $capability The capability to scan for in the categories
      * @param int|null $userid Userid to use in check (Use current user if null or empty)
-     * @return boolean
+     * @return bool
      */
     public static function has_capability_in_any_category($capability, $userid=null ) {
         global $USER;
diff --git a/classes/local/randomimage.php b/classes/local/randomimage.php
index fd375c2..22a730a 100644
--- a/classes/local/randomimage.php
+++ b/classes/local/randomimage.php
@@ -74,7 +74,6 @@ class randomimage {
      * Create a random polygon with number of points between 0 & $maxpts
      * @param  \GdImage  $im      The image reource
      * @param  int  $maxpts Max number of point to use
-     * @return void
      */
     private function random_polygon($im, int $maxpts = 20) {
         $color = imagecolorallocatealpha($im, ...$this->random_color_alpha());
@@ -86,7 +85,6 @@ class randomimage {
     /**
      * Creates a random arc of a random color
      * @param \GdImage $im The image resource
-     * @return void
      */
     private function random_arc($im) {
         $cx = \random_int(0, $this->width);
@@ -102,7 +100,7 @@ class randomimage {
 
     /**
      * Generates an array of random alpha color values.
-     * @return Array [r, g, b, a]
+     * @return array [r, g, b, a]
      */
     private function random_color_alpha(): Array {
         return [
@@ -116,7 +114,7 @@ class randomimage {
     /**
      * Generates a set of random points for a polygon [x1, y1, x2, y2, ...]
      * @param  integer $length Number of sets of points to generate
-     * @return Array           The resulting array of points
+     * @return array           The resulting array of points
      */
     private function random_pts($length): Array {
         $pts = [];
@@ -159,8 +157,12 @@ class randomimage {
             }
         }
         $this->tempfile = \tempnam("/tmp", "tsp");
-        imagepng($im, $this->tempfile);
-        imagedestroy($im);
+        if (is_object($im)) {
+            imagepng($im, $this->tempfile);
+        }
+        if (is_object($im)) {
+            imagedestroy($im);
+        }
     }
 
     /**
@@ -168,7 +170,12 @@ class randomimage {
      * @return string
      */
     public function content() {
-        return $this->content = \file_get_contents($this->tempfile);
+        $this->content = \file_get_contents($this->tempfile);
+        if (is_string($this->content)) {
+            return $this->content;
+        } else {
+            return "";
+        }
     }
 
     /**
diff --git a/classes/local/ungradedscanners/quiz_scanner.php b/classes/local/ungradedscanners/quiz_scanner.php
index e88ff17..8a3eafa 100644
--- a/classes/local/ungradedscanners/quiz_scanner.php
+++ b/classes/local/ungradedscanners/quiz_scanner.php
@@ -32,6 +32,7 @@ require_once($CFG->dirroot.'/question/engine/states.php'); // For reading questi
 class quiz_scanner extends scanner_base {
     /**
      * Retrieve the ungraded submissions in this activity
+     * @return array
      */
     protected function get_ungraded_submissions() {
         // Count all users who have one or more questions that still need grading.
diff --git a/classes/period.php b/classes/period.php
index 2f260ce..028a198 100644
--- a/classes/period.php
+++ b/classes/period.php
@@ -93,7 +93,7 @@ class period {
             // Or specified duration of the page and the sequence of the periods .
             $pcount = $page->periods();
             $ystart = $page->startdate()->getTimestamp();
-            $yend = $page->enddate()->getTimestamp();
+            $yend = ((object)($page->enddate(true)))->getTimestamp();
 
             // Estimate the period's timing to make a reasonable first guess.
             $ydelta = $yend - $ystart;
diff --git a/classes/privacy/provider.php b/classes/privacy/provider.php
index 8f07d6f..1b04603 100644
--- a/classes/privacy/provider.php
+++ b/classes/privacy/provider.php
@@ -148,8 +148,10 @@ class provider implements   \core_privacy\local\metadata\provider,
         $context = \context_system::instance();
         $subcontext = ["invitations"];
 
-        writer::with_context($context)
-            ->export_data($subcontext, (object)["recipient" => $invit->name, "email" => $invit->email]);
+        $data = new \stdClass;
+        $data->recipient = $invit->name;
+        $data->email = $invit->email;
+        writer::with_context($context)->export_data($subcontext, $data);
 
     }
 
@@ -161,8 +163,10 @@ class provider implements   \core_privacy\local\metadata\provider,
         $context = \context_system::instance();
         $subcontext = ["studyplans"];
 
-        writer::with_context($context)
-            ->export_data($subcontext, (object)["fullname" => $studyplan->fullname, "shortname" => $studyplan->shortname]);
+        $data = new \stdClass;
+        $data->fullname = $studyplan->fullname;
+        $data->shortname = $studyplan->shortname;
+        writer::with_context($context)->export_data($subcontext, $data);
 
     }
 
diff --git a/classes/reportinvite_form.php b/classes/reportinvite_form.php
index 3c0654b..70225c7 100644
--- a/classes/reportinvite_form.php
+++ b/classes/reportinvite_form.php
@@ -74,7 +74,7 @@ class reportinvite_form extends moodleform {
 
     /**
      * Get supplied user data
-     * @return stdClass The supplied data
+     * @return object The supplied data
      */
     public function get_data() {
         global $DB, $USER;
diff --git a/classes/reportservice.php b/classes/reportservice.php
index d349f50..247a134 100644
--- a/classes/reportservice.php
+++ b/classes/reportservice.php
@@ -76,7 +76,7 @@ class reportservice extends \external_api {
      * @param int $pageid ID of user to check specific info for
      * @param int|null $firstperiod First period to include in report
      * @param int|null $lastperiod Last period to include in report
-     * @return object
+     * @return array
      */
     public static function get_report_structure($pageid, $firstperiod=null, $lastperiod=null) {
         $page = studyplanpage::find_by_id($pageid);
diff --git a/classes/studentstudyplanservice.php b/classes/studentstudyplanservice.php
index 5bdc017..8e51cc5 100644
--- a/classes/studentstudyplanservice.php
+++ b/classes/studentstudyplanservice.php
@@ -114,7 +114,7 @@ class studentstudyplanservice extends \external_api {
      * Get a specific studyplan for a given user
      * @param int $userid ID of user to check specific info for
      * @param int $studyplanid ID of studyplan to view
-     * @return array
+     * @return array|null
      */
     public static function get_user_studyplan($userid, $studyplanid) {
         global $CFG, $DB;
@@ -162,7 +162,7 @@ class studentstudyplanservice extends \external_api {
      * Get a specific studyplan page for a given user
      * @param int $userid ID of user to check specific info for
      * @param int $pageid ID of studyplan to view
-     * @return array
+     * @return array|null
      */
     public static function get_user_page($userid, $pageid) {
         global $CFG, $DB;
diff --git a/classes/studyline.php b/classes/studyline.php
index 41dc9a5..888cab8 100644
--- a/classes/studyline.php
+++ b/classes/studyline.php
@@ -657,7 +657,7 @@ class studyline {
     /**
      * List the course id is linked in this studyplan
      * Used for cohort enrolment cascading
-     * @return int[]
+     * @return array
      */
     public function get_linked_course_ids(): array {
         global $DB;
@@ -845,7 +845,6 @@ class studyline {
      * @param array $model Decoded array
      * @param array $itemtranslation Link to array to map old item ids to new item ids for connection matching
      * @param array $connections Link to array of connections between item
-     * @return null
      */
     public function import_studyitems(array $model, array &$itemtranslation, array &$connections) {
         global $DB;
diff --git a/classes/studyplan.php b/classes/studyplan.php
index c492593..2064e67 100644
--- a/classes/studyplan.php
+++ b/classes/studyplan.php
@@ -167,37 +167,40 @@ class studyplan {
 
         if (count($files) > 0) {
             $file = array_shift($files);
-            if ($file->get_filename() == ".") {
+
+            if (is_object($file) && $file->get_filename() == ".") {
                 // Get next file if the first is the directory itself.
                 $file = array_shift($files);
             }
 
-            $url = \moodle_url::make_pluginfile_url(
-                $file->get_contextid(),
-                $file->get_component(),
-                $file->get_filearea(),
-                $file->get_itemid(),
-                $file->get_filepath(),
-                $file->get_filename(),
-                false                     // Do not force download of the file.
-            );
-        } else {
-            // Try the configured default in settings.
-            $defaulticon = get_config('local_treestudyplan', 'defaulticon');
-            if (empty($defaulticon)) {
-                   // Fall back to the standard (ugly) default image.
-                   $url = new \moodle_url($CFG->wwwroot . "/local/treestudyplan/pix/default_icon.png");
-            } else {
+            if (is_object($file)) {
                 $url = \moodle_url::make_pluginfile_url(
-                            \context_system::instance()->id,
-                            'local_treestudyplan',
-                            'defaulticon',
-                            0,
-                            "/",
-                            $defaulticon
-                        );
+                    $file->get_contextid(),
+                    $file->get_component(),
+                    $file->get_filearea(),
+                    $file->get_itemid(),
+                    $file->get_filepath(),
+                    $file->get_filename(),
+                    false                     // Do not force download of the file.
+                );
+                return $url->out;
             }
+        }
 
+        // Try the configured default in settings.
+        $defaulticon = get_config('local_treestudyplan', 'defaulticon');
+        if (empty($defaulticon)) {
+                // Fall back to the standard (ugly) default image.
+                $url = new \moodle_url($CFG->wwwroot . "/local/treestudyplan/pix/default_icon.png");
+        } else {
+            $url = \moodle_url::make_pluginfile_url(
+                        \context_system::instance()->id,
+                        'local_treestudyplan',
+                        'defaulticon',
+                        0,
+                        "/",
+                        $defaulticon
+                    );
         }
         return $url->out();
     }
@@ -735,7 +738,7 @@ class studyplan {
 
     /**
      * Retrieve the users linked to this studyplan.
-     * @return stdClass[] User objects
+     * @return \stdClass[] User objects
      */
     public function find_linked_users(): array {
         global $DB;
@@ -787,7 +790,7 @@ class studyplan {
 
     /**
      * Check if this studyplan is linked to a particular user
-     * @param bool|stdClass $user The userid or user record of the user
+     * @param int|stdClass $user The userid or user record of the user
      */
     public function has_linked_user($user) {
         if (is_int($user)) {
@@ -805,7 +808,7 @@ class studyplan {
 
     /**
      * Check if this studyplan is linked to a particular user
-     * @param bool|stdClass|null $user The userid or user record of the user Leave empty to check current user.
+     * @param int|stdClass|null $user The userid or user record of the user Leave empty to check current user.
      */
     public function is_coach($user=null) {
         global $DB, $USER;
@@ -968,9 +971,9 @@ class studyplan {
 
         // Next, copy the studylines.
         $timeless = \get_config("local_treestudyplan", "timelessperiods");
-        if (!$timeless && $newstartdate) {
+        $oldstart = $this->startdate();
+        if (!$timeless && $newstartdate && is_object($oldstart)) {
             $newstart = new \DateTime(date("Y-m-d", $newstartdate));
-            $oldstart = $this->startdate();
             $timeoffset = $oldstart->diff($newstart);
         } else {
             $timeoffset = new \DateInterval("P0D");
diff --git a/classes/studyplanpage.php b/classes/studyplanpage.php
index d16bef5..a1b099e 100644
--- a/classes/studyplanpage.php
+++ b/classes/studyplanpage.php
@@ -509,7 +509,7 @@ class studyplanpage {
             'description' => $this->r->description,
             'pages' => $this->r->pages,
             'startdate' => $this->startdate()->add($timeoffset)->format("Y-m-d"),
-            'enddate' => empty($this->r->enddate) ? null : ($this->enddate()->add($timeoffset)->format("Y-m-d")),
+            'enddate' => empty($this->r->enddate) ? null : (((object)$this->enddate(true))->add($timeoffset)->format("Y-m-d")),
         ]);
 
         // Copy any files related to this page.
diff --git a/classes/studyplanservice.php b/classes/studyplanservice.php
index e6bed48..0a63abb 100644
--- a/classes/studyplanservice.php
+++ b/classes/studyplanservice.php
@@ -122,7 +122,7 @@ class studyplanservice extends \external_api {
     /**
      * Get editor model for specific studyplan
      * @param int $id Id of studyplan
-     * @return array
+     * @return array|null
      */
     public static function get_studyplan_map($id) {
         if (isset($id) && $id > 0) {
@@ -1224,64 +1224,66 @@ class studyplanservice extends \external_api {
                     $studyitem = new studyitem($itemr->id);
                     if ($studyitem->valid() && $studyitem->type() == studyitem::COURSE) {
                         $courseinfo = $studyitem->getcourseinfo();
-                        $gradables = gradeinfo::list_studyitem_gradables($studyitem);
+                        if(is_object($courseinfo)){
+                            $gradables = gradeinfo::list_studyitem_gradables($studyitem);
 
-                        $gradelist = [];
-                        foreach ($gradables as $g) {
-                            $gi = $g->get_gradeitem();
+                            $gradelist = [];
+                            foreach ($gradables as $g) {
+                                $gi = $g->get_gradeitem();
 
-                            // Only change items that do not yet have grades.
-                            // Otherwise we will need to implement grade recalculations and it is not worth the trouble. .
-                            // If grades are given, you likely don't want to change it like this anyway.
+                                // Only change items that do not yet have grades.
+                                // Otherwise we will need to implement grade recalculations and it is not worth the trouble. .
+                                // If grades are given, you likely don't want to change it like this anyway.
 
-                            if (!$gi->has_grades()) {
-                                $gi->gradetype = GRADE_TYPE_SCALE;
-                                $gi->scaleid = $scale->id;
-                                $gi->grademin = 1;
-                                $gi->grademax = $scalemax;
-                                $gi->gradepass = $scalepass;
+                                if (!$gi->has_grades()) {
+                                    $gi->gradetype = GRADE_TYPE_SCALE;
+                                    $gi->scaleid = $scale->id;
+                                    $gi->grademin = 1;
+                                    $gi->grademax = $scalemax;
+                                    $gi->gradepass = $scalepass;
 
-                                // Update, signalling with our signature and bulkupdate.
-                                $result = $gi->update("local/treestudyplan");
+                                    // Update, signalling with our signature and bulkupdate.
+                                    $result = $gi->update("local/treestudyplan");
 
-                                $debug = "";
-                                if ($result) {
-                                    $updated = "converted";
-                                } else {
-                                    $updated = "error";
-                                }
+                                    $debug = "";
+                                    if ($result) {
+                                        $updated = "converted";
+                                    } else {
+                                        $updated = "error";
+                                    }
 
-                                // Next update the activity's table if it has a grade field.
-                                // Grade is generally set to the negative scale id if it is a scale.
-                                $tablename = $gi->itemmodule;
-                                $fieldname = "grade";
-                                if ($result && $gi->itemtype == "mod" && $dbman->table_exists($tablename)) {
-                                    if ($dbman->field_exists($tablename, $fieldname)) {
-                                        $gradevalue = intval(0 - ($scale->id));
-                                        try {
-                                            $DB->set_field($tablename, $fieldname, $gradevalue, ["id" => $gi->iteminstance]);
-                                        } catch (\dml_exception $x) {
-                                            $updated = "fail";
-                                            $debug = strval($x);
+                                    // Next update the activity's table if it has a grade field.
+                                    // Grade is generally set to the negative scale id if it is a scale.
+                                    $tablename = $gi->itemmodule;
+                                    $fieldname = "grade";
+                                    if ($result && $gi->itemtype == "mod" && $dbman->table_exists($tablename)) {
+                                        if ($dbman->field_exists($tablename, $fieldname)) {
+                                            $gradevalue = intval(0 - ($scale->id));
+                                            try {
+                                                $DB->set_field($tablename, $fieldname, $gradevalue, ["id" => $gi->iteminstance]);
+                                            } catch (\dml_exception $x) {
+                                                $updated = "fail";
+                                                $debug = strval($x);
+                                            }
                                         }
                                     }
+
+                                } else {
+                                    $updated = "skipped";
                                 }
 
-                            } else {
-                                $updated = "skipped";
+                                $gradelist[] = [
+                                    'name' => $gi->itemname,
+                                    'changed' => $updated,
+                                    'debug' => $debug,
+                                ];
                             }
 
-                            $gradelist[] = [
-                                'name' => $gi->itemname,
-                                'changed' => $updated,
-                                'debug' => $debug,
+                            $list[] = [
+                                'course' => $courseinfo->simple_model(),
+                                'grades' => $gradelist,
                             ];
                         }
-
-                        $list[] = [
-                            'course' => $courseinfo->simple_model(),
-                            'grades' => $gradelist,
-                        ];
                     }
                 }
             }
@@ -2216,7 +2218,7 @@ class studyplanservice extends \external_api {
 
     /**
      * Count the number of templates available
-     * @return array
+     * @return int
      */
     public static function count_templates() {
         \external_api::validate_context(\context_system::instance());
diff --git a/classes/teachingfinder.php b/classes/teachingfinder.php
index ae1226c..b2a6cc4 100644
--- a/classes/teachingfinder.php
+++ b/classes/teachingfinder.php
@@ -177,7 +177,7 @@ class teachingfinder {
 
     /**
      * List of recognized teacher id's
-     * @return intp[]
+     * @return int[]
      */
     public static function list_teacher_ids() {
         global $DB;
diff --git a/classes/utilityservice.php b/classes/utilityservice.php
index f72ee21..b49a3d7 100644
--- a/classes/utilityservice.php
+++ b/classes/utilityservice.php
@@ -78,7 +78,6 @@ class utilityservice extends \external_api {
      * Returns description of get_mform parameters
      *
      * @return \external_function_parameters
-     * @since Moodle 3.1
      */
     public static function get_mform_parameters() {
         return new \external_function_parameters([
@@ -122,7 +121,6 @@ class utilityservice extends \external_api {
      * Returns description of get_mform() result value
      *
      * @return \core_external\external_description
-     * @since Moodle 3.1
      */
     public static function get_mform_returns() {
         return new \external_single_structure(
@@ -196,7 +194,7 @@ class utilityservice extends \external_api {
 
     /**
      * Submit specified form data into form
-     * @return array Success/fail structure
+     * @return array of settings
      */
     public static function getsettings() {
         global $CFG;