Merge branch '6.x' into 7.x

Eloquent/Concerns/HasRelationships.php

@@ -256,7 +256,7 @@ public function morphTo($name = null, $type = null, $id = null, $ownerKey = null
         // If the type value is null it is probably safe to assume we're eager loading
         // the relationship. In this case we'll just pass in a dummy query where we
         // need to remove any eager loads that may already be defined on a model.
-        return empty($class = $this->{$type})
+        return is_null($class = $this->{$type}) || $class === ''
                     ? $this->morphEagerTo($name, $type, $id, $ownerKey)
                     : $this->morphInstanceTo($class, $name, $type, $id, $ownerKey);
     }