code: def test_firstresult_returns_none(pm):
      """If None results are returned by underlying implementations ensure
      the multi-call loop returns a None value.
      """
  
      class Api(object):
          @hookspec(firstresult=True)
          def hello(self, arg):
              "api hook 1"
  
      pm.add_hookspecs(Api)
  
      class Plugin1(object):
          @hookimpl
          def hello(self, arg):
              return None
  
      pm.register(Plugin1())
      res = pm.hook.hello(arg=3)
      assert res is None
  
file_path: catboost/contrib/python/pluggy/py2/tests/test_invocations.py
imports: import pytest
  from pluggy import PluginValidationError, HookimplMarker, HookspecMarker
label_desc: Use image node_id 7 for calling a global function with example usage: test_firstresult_returns_none(pm) and returns: None