replace None with 'null' in query paramters

Requests skips parameters that are None.
Map 'null' string to None python type for a more native coding

pynetbox/core/endpoint.py

@@ -285,8 +285,9 @@ def filter(self, *args, **kwargs):
         offset = kwargs.pop("offset") if "offset" in kwargs else None
         if limit == 0 and offset is not None:
             raise ValueError("offset requires a positive limit value")
+        filters = {x: y if y is not None else "null" for x, y in kwargs.items()}
         req = Request(
-            filters=kwargs,
+            filters=filters,
             base=self.url,
             token=self.token,
             http_session=self.api.http_session,

tests/unit/test_endpoint.py

@@ -24,6 +24,14 @@ def test_filter_invalid_pagination_args(self):
         with self.assertRaises(ValueError) as _:
             test_obj.filter(offset=1)
 
+    def test_filter_replace_none_with_null(self):
+        api = Mock(base_url="http://localhost:8000/api")
+        app = Mock(name="test")
+        test_obj = Endpoint(api, app, "test")
+        test = test_obj.filter(name=None, id=0)
+
+        self.assertEqual(test.request.filters, {"name": "null", "id": 0})
+
     def test_all_invalid_pagination_args(self):
 
         api = Mock(base_url="http://localhost:8000/api")