Show error message if search query tests for NULL using comparison operators

flask_restless/manager.py

@@ -204,7 +204,7 @@ def create_api_blueprint(self, model, methods=READONLY_METHODS,
                              post_form_preprocessor=None,
                              preprocessors=None, postprocessors=None,
                              primary_key=None):
-        """Creates an returns a ReSTful API interface as a blueprint, but does
+        """Creates and returns a ReSTful API interface as a blueprint, but does
         not register it on any :class:`flask.Flask` application.
 
         The endpoints for the API for ``model`` will be available at

flask_restless/search.py

@@ -342,7 +342,9 @@ def _create_operation(model, fieldname, operator, argument, relation=None):
         if numargs == 1:
             return opfunc(field)
         if argument is None:
-            raise TypeError
+            msg = ('To compare a value to NULL, use the is_null/is_not_null '
+                'operators.')
+            raise TypeError(msg)
         if numargs == 2:
             return opfunc(field, argument)
         return opfunc(field, argument, fieldname)

tests/test_search.py

@@ -145,6 +145,9 @@ def test_operators(self):
         d = dict(filters=[dict(name='birth_date', op='is_not_null')])
         result = search(self.session, self.Person, d)
         assert result.count() == 1
+        d = dict(filters=[dict(name='birth_date', op='eq', val=None)])
+        assert_raises(TypeError, search, self.session, self.Person, d)
+
 
     def test_desc_and_asc(self):
         """Tests for the ``"desc"`` and ``"asc"`` operators."""