Changed exception message.

Sync/Extractor/DoctrineExtractor.php

@@ -83,7 +83,7 @@ public function extract(BaseDiffItem $item)
                         $this->getShopIds()
                     );
                 } elseif (empty($statements)) {
-                    throw new \LogicException('Relation does not have any effect');
+                    throw new \LogicException('Missing related statements or no document type set in relation.');
                 }
 
                 foreach ($statements as $statement) {