Extend error message when missing subrecord column id

extension/Classes/Core/AbstractBuildForm.php

@@ -2259,7 +2259,7 @@ abstract class AbstractBuildForm {
 
             if (!isset($formElement[FE_SQL1][0][$nameColumnId])) {
                 throw new \UserFormException(
-                    json_encode([ERROR_MESSAGE_TO_USER => "Missing column [_]$nameColumnId in subrecord query", ERROR_MESSAGE_TO_DEVELOPER => $this->$formElement[FE_SQL1]]),
+                    json_encode([ERROR_MESSAGE_TO_USER => "Missing column [_]$nameColumnId in subrecord query", ERROR_MESSAGE_TO_DEVELOPER => $formElement[FE_SQL1]]),
                     ERROR_SUBRECORD_MISSING_COLUMN_ID);
             }
         }