bug fix

Author: jchanvfx

NodeGraphQt/base/node.py

@@ -784,7 +784,7 @@ def add_input(self, name='input', multi_input=False, display_name=True,
                 'port name "{}" already registered.'.format(name))
 
         port_args = [name, multi_input, display_name]
-        if painter_func and not callable(painter_func):
+        if painter_func and callable(painter_func):
             port_args.append(painter_func)
         view = self.view.add_input(*port_args)