Version 4.7.0

applications/nexus/sources/Invoice/Item/Item.php

@@ -372,7 +372,7 @@ abstract class _Item
 	{
 		/* If one is set to be associated with something in the cart and the other is set to be associated
 		with an existing purchase, trying to compare those will throw an error */
-		if ( $item->parent or $this->parent )
+		if ( isset( $item->parent ) and isset( $this->parent ) )
 		{			
 			if ( \gettype( $this->parent ) != \gettype( $item->parent ) )
 			{