fixed belongs_to eager loading bug when parent does not exist.

system/db/eloquent/hydrator.php

@@ -200,10 +200,13 @@ class Hydrator {
 		// Match the child models with their parent by ID.
 		// -----------------------------------------------------
 		foreach ($parents as &$parent)
+		{
+			if (array_key_exists($parent->$relating_key, $children))
 			{
 				$parent->ignore[$include] = $children[$parent->$relating_key];
 			}
 		}
+	}
 
 	/**
 	 * Eagerly load a many-to-many relationship.