{
             _tree = tree;
             _location = location;
-            _typeMap = _tree.Types.OfType<AbstractNode>().ToDictionary(t => t.Name, t => (AbstractNode?)t);
+            _typeMap = _tree.Types.OfType<AbstractNode>().ToDictionary(t => t.Name, t => t);
             _typeMap.Add("IOperation", null);
         }