Issue #3270876 by sonfd, hmendes, jwilson3: Check if $form_object->getEntity() is public

label_help.module

@@ -47,6 +47,11 @@ function label_help_form_alter(&$form, &$form_state, $form_id) {
   if (!method_exists($form_object, 'getEntity')) {
     return;
   }
+  $method = new ReflectionMethod($form_object, 'getEntity');
+  if (!$method->isPublic()) {
+    return;
+  }
+
   $form_entity = $form_object->getEntity();
   if (!method_exists($form_entity, 'getFieldDefinition')) {
     return;