when adding a node makes the type mandatory, only add the node to instance models if it does not exists there yet

evolution/node_ops.py

@@ -22,9 +22,10 @@ class NodeAdd(object):
             if check_if_last:
                 if commons.is_type_mandatory(node_type):
                     print("Type {} became mandatory, adding it to instance models ...".format(node_type))
-                    # local add made type mandatory, so need to add to instance models
+                    # local add made type mandatory, so need to add to instance models (if not exists already)
                     for im in commons.all_instance_models():
-                        self.execute(im, node_type, local=True, check_if_last=False)
+                        if not commons.all_nodes_with_type(im, self._node_type):
+                            self.execute(im, node_type, local=True, check_if_last=False)
 
         else:
             for m in commons.all_models():