diff --git a/classes/submission/assign.php b/classes/submission/assign.php
index f14367d..a4c7ed2 100644
--- a/classes/submission/assign.php
+++ b/classes/submission/assign.php
@@ -61,7 +61,7 @@ protected function set_module_instance() {
      * @throws \dml_exception
      * @throws \moodle_exception
      */
-    protected function set_submission_data() {
+    protected function set_submission_data(): void {
         $this->submissiondata = $this->get_assign_submission();
     }
 
diff --git a/classes/submission/hvp.php b/classes/submission/hvp.php
index 0928243..13afa20 100644
--- a/classes/submission/hvp.php
+++ b/classes/submission/hvp.php
@@ -63,7 +63,6 @@ protected function set_module_instance() {
      * {@see \local_sitsgradepush\manager::push_submission_log_to_sits()}
      * We get the item time from the gradebook.  (We don't have submissions stored in the mod_hvp local tables).
      * @return void
-     * @see
      */
     protected function set_submission_data(): void {
         $grades = grade_get_grades(
diff --git a/classes/submission/quiz.php b/classes/submission/quiz.php
index cf5c133..bc317e4 100644
--- a/classes/submission/quiz.php
+++ b/classes/submission/quiz.php
@@ -63,7 +63,7 @@ protected function set_module_instance() {
      * @throws \dml_exception
      * @throws \moodle_exception
      */
-    protected function set_submission_data() {
+    protected function set_submission_data(): void {
         $this->submissiondata = $this->get_best_attempt();
     }
 
diff --git a/classes/submission/submission.php b/classes/submission/submission.php
index 6b1e730..f9cc1b7 100644
--- a/classes/submission/submission.php
+++ b/classes/submission/submission.php
@@ -166,6 +166,14 @@ public function get_submission_data() {
         return $this->submissiondata;
     }
 
+    /**
+     * Set submission data.
+     * The submission log transfer will be skipped without this data.
+     * {@see \local_sitsgradepush\manager::push_submission_log_to_sits()}
+     * @return void
+     */
+    abstract protected function set_submission_data(): void;
+
     /**
      * Get ISO 8601 format datetime.
      *
diff --git a/classes/submission/turnitintooltwo.php b/classes/submission/turnitintooltwo.php
index c9a4273..3afb6db 100644
--- a/classes/submission/turnitintooltwo.php
+++ b/classes/submission/turnitintooltwo.php
@@ -61,7 +61,7 @@ protected function set_module_instance() {
      * @throws \dml_exception
      * @throws \moodle_exception
      */
-    protected function set_submission_data() {
+    protected function set_submission_data(): void {
         $this->submissiondata = $this->get_turnitintooltwo_submission();
     }