avoid NoneType exception for None handler (#8)

Author: marthjod

python_grpc_prometheus/prometheus_server_interceptor.py

@@ -49,6 +49,8 @@ class PromServerInterceptor(grpc.ServerInterceptor):
     def intercept_service(self, continuation, handler_call_details):
 
         handler = continuation(handler_call_details)
+        if handler is None:
+            return handler
 
         # only support unary
         if handler.request_streaming or handler.response_streaming:

tests/test_prometheus_server_interceptor.py

@@ -1,7 +1,7 @@
 from unittest import TestCase
 from unittest.mock import Mock
 
-from nose.tools import assert_equal
+from nose.tools import assert_equal, assert_is_none
 from parameterized import parameterized
 
 import requests
@@ -44,6 +44,11 @@ def test_intercept_service_method_name_too_short(self, method):
         self.psi.intercept_service(mock_continuation, mock_handler_call_details)
         assert_equal(2, mock_continuation.call_count)
 
+    def test_none_handler(self):
+        mock_continuation = Mock(return_value=None)
+
+        ret = self.psi.intercept_service(mock_continuation, Mock())
+        assert_is_none(ret)
 
 class TestServiceLatencyInterceptor(TestCase):
     def setUp(self):