Allow null option for properties

The Swagger specification in version 2 doesn't support 'null' as
property value. This adds a vendor extension 'x-nullable' which
allows properties to be 'null' if set to 'true'.
See OAI/OpenAPI-Specification#229

bravado_core/schema.py

@@ -38,6 +38,10 @@ def is_param_spec(swagger_spec, schema_object_spec):
     return 'in' in swagger_spec.deref(schema_object_spec)
 
 
+def is_prop_nullable(swagger_spec, schema_object_spec):
+    return swagger_spec.deref(schema_object_spec).get('x-nullable', False)
+
+
 def is_ref(spec):
     return is_dict_like(spec) and '$ref' in spec
 

bravado_core/swagger20_validator.py

@@ -5,6 +5,7 @@
 from jsonschema.validators import Draft4Validator
 
 from bravado_core.schema import is_param_spec
+from bravado_core.schema import is_prop_nullable
 from bravado_core.schema import is_required
 from swagger_spec_validator.ref_validators import in_scope
 
@@ -18,8 +19,10 @@
 def type_validator(swagger_spec, validator, types, instance, schema):
     """Skip the `type` validator when a Swagger parameter value is None.
     Otherwise it will fail with a "None is not a valid type" failure instead
-    of letting the downstream `required_validator` do its job. In all other
-    cases, delegate to the existing Draft4 `type` validator.
+    of letting the downstream `required_validator` do its job.
+    Also skip when a Swagger property value is None and the schema contains
+    the extension field `x-nullable` set to True.
+    In all other cases, delegate to the existing Draft4 `type` validator.
 
     :param swagger_spec: needed for access to deref()
     :type swagger_spec: :class:`bravado_core.spec.Spec`
@@ -32,7 +35,8 @@ def type_validator(swagger_spec, validator, types, instance, schema):
     :param schema: swagger spec for the object
     :type schema: dict
     """
-    if is_param_spec(swagger_spec, schema) and instance is None:
+    if (is_param_spec(swagger_spec, schema) or
+            is_prop_nullable(swagger_spec, schema)) and instance is None:
         return
 
     for error in _validators.type_draft4(validator, types, instance, schema):

tests/schema/is_prop_nullable_test.py

@@ -0,0 +1,48 @@
+from bravado_core.schema import is_prop_nullable
+from bravado_core.spec import Spec
+
+
+def test_true(minimal_swagger_spec):
+    prop_spec = {
+        'type': 'string',
+        'x-nullable': True,
+    }
+    assert is_prop_nullable(minimal_swagger_spec, prop_spec)
+
+
+def test_false(minimal_swagger_spec):
+    prop_spec = {
+        'type': 'string',
+    }
+    assert not is_prop_nullable(minimal_swagger_spec, prop_spec)
+
+
+def test_false_explicit(minimal_swagger_spec):
+    prop_spec = {
+        'type': 'string',
+        'x-nullable': False,
+    }
+    assert not is_prop_nullable(minimal_swagger_spec, prop_spec)
+
+
+def test_ref_true(minimal_swagger_dict):
+    minimal_swagger_dict['definitions'] = {
+        'Pet': {
+            'type': 'object',
+            'x-nullable': True,
+        }
+    }
+    param_spec = {'$ref': '#/definitions/Pet'}
+    swagger_spec = Spec.from_dict(minimal_swagger_dict)
+    assert is_prop_nullable(swagger_spec, param_spec)
+
+
+def test_ref_false(minimal_swagger_dict):
+    minimal_swagger_dict['definitions'] = {
+        'Pet': {
+            'type': 'object',
+        }
+    }
+    param_spec = {'$ref': '#/definitions/Pet'}
+    swagger_spec = Spec.from_dict(minimal_swagger_dict)
+    assert not is_prop_nullable(swagger_spec, param_spec)

tests/swagger20_validator/type_validator_test.py

@@ -34,3 +34,25 @@ def test_validate_when_not_a_parameter_schema(m_draft4_type_validator,
             string_schema)
     list(type_validator(minimal_swagger_spec, *args))
     m_draft4_type_validator.assert_called_once_with(*args)
+
+
+@patch('jsonschema._validators.type_draft4')
+def test_skip_when_nullable_property_schema_and_value_is_None(
+        m_draft4_type_validator, minimal_swagger_spec):
+    param_schema = {'name': 'foo', 'x-nullable': True, 'type': 'string'}
+    type_validator(
+        minimal_swagger_spec,
+        validator=None,
+        types=param_schema['type'],
+        instance=None,  # property value
+        schema=param_schema)
+    assert m_draft4_type_validator.call_count == 0
+
+
+@patch('jsonschema._validators.type_draft4')
+def test_validate_when_not_nullable_property_schema_and_value_is_None(
+        m_draft4_type_validator, minimal_swagger_spec):
+    param_schema = {'name': 'foo', 'x-nullable': False, 'type': 'string'}
+    args = (None, param_schema['type'], None, param_schema)
+    type_validator(minimal_swagger_spec, *args)
+    m_draft4_type_validator.assert_called_once_with(*args)