Allow 0 id for Entity

When using a 0 id, it's throwing InvalidArgumentException (Binding entities to query parameters only allowed for entities that have an identifier.)

lib/Doctrine/ORM/AbstractQuery.php

@@ -281,7 +281,7 @@ abstract class AbstractQuery
 
         $value = $values[$class->getSingleIdentifierFieldName()];
 
-        if ( ! $value) {
+        if ( ! isset($value)) {
             throw new \InvalidArgumentException(
                 "Binding entities to query parameters only allowed for entities that have an identifier."
             );