MDL-52046 reportbuilder: Support null return from checkbox callback

.upgradenotes/MDL-52046-2024061805141748.yml

@@ -0,0 +1,8 @@
+issueNumber: MDL-52046
+notes:
+  core_reportbuilder:
+    - message: >-
+        The return type of the `set_checkbox_toggleall` callback, defined by
+        system reports, can now be null. Use if the checkbox should not be shown
+        for the row.
+      type: improved

reportbuilder/classes/system_report.php

@@ -143,7 +143,7 @@ final public function get_base_fields(): array {
      * Define toggle all checkbox for the report, required row data should be defined by calling {@see add_base_fields}
      *
      * @param callable $callback Callback to return value/label for each checkbox, implementing the following signature:
-     *      function(stdClass $row): array containing value/label pair
+     *      function(stdClass $row): ?array containing value/label pair, or null if the checkbox should not be shown for the row
      */
     final protected function set_checkbox_toggleall(callable $callback): void {
         $this->checkboxcallback = $callback;
@@ -166,7 +166,11 @@ final public function get_checkbox_toggleall(bool $ismaster, ?stdClass $row = nu
             $value = '';
             $label = get_string('selectall');
         } else {
-            [$value, $label] = ($this->checkboxcallback)($row);
+            $checkboxdata = ($this->checkboxcallback)($row);
+            if ($checkboxdata === null) {
+                return null;
+            }
+            [$value, $label] = $checkboxdata;
         }
 
         return new checkbox_toggleall('report-select-all', $ismaster, [