Properly handle empty enums

Author: noirbizarre

CHANGELOG.rst

@@ -9,6 +9,7 @@ Current
 - Fix missing changelog inprevious release
 - Ensure definitions with both `$ref` and description (or other property) output is valid (using `allOf`)
 - Added initial specifications schemas and validation support
+- Ensure empty enums are not serialized (to have a valid specification)
 
 0.12.0 (2018-09-27)
 -------------------

flask_restplus/fields.py

@@ -379,7 +379,8 @@ def format(self, value):
     def schema(self):
         enum = self._v('enum')
         schema = super(String, self).schema()
-        schema.update(enum=enum)
+        if enum:
+            schema.update(enum=enum)
         if enum and schema['example'] is None:
             schema['example'] = enum[0]
         return schema

tests/test_fields.py

@@ -195,12 +195,23 @@ def test_with_enum(self):
         assert not field.required
         assert field.__schema__ == {'type': 'string', 'enum': enum, 'example': enum[0]}
 
+    def test_with_empty_enum(self):
+        field = fields.String(enum=[])
+        assert not field.required
+        assert field.__schema__ == {'type': 'string'}
+
     def test_with_callable_enum(self):
         enum = lambda: ['A', 'B', 'C']  # noqa
         field = fields.String(enum=enum)
         assert not field.required
         assert field.__schema__ == {'type': 'string', 'enum': ['A', 'B', 'C'], 'example': 'A'}
 
+    def test_with_empty_callable_enum(self):
+        enum = lambda: []  # noqa
+        field = fields.String(enum=enum)
+        assert not field.required
+        assert field.__schema__ == {'type': 'string'}
+
     def test_with_default(self):
         field = fields.String(default='aaa')
         assert field.__schema__ == {'type': 'string', 'default': 'aaa'}