Fixed the check for self.root when deleting a node

state/modelverse_state/main.py

@@ -319,7 +319,7 @@ class ModelverseState(object):
             return ([self.edges[e][0] for e in matches], status.SUCCESS)
 
     def delete_node(self, node):
-        if node is self.root:
+        if node == self.root:
             return (None, status.FAIL_DN_UNKNOWN)
 
         if node not in self.nodes: