do not need deep copy for null state

DecMCTS.py

@@ -178,7 +178,7 @@ class Tree:
 
 
     def _null_state(self, state):
-        temp = deepcopy(state)
+        temp = copy(state)
         temp[self.id] = self.graph.node[1]["state"] # Null state is if robot still at root node
         return temp