Ignoring none field if it is not required.

.gitignore

@@ -44,3 +44,5 @@ docs/_build/
 
 # Vim swap files
 *.swp
+/venv/
+/.idea/

serpy/serializer.py

@@ -115,6 +115,9 @@ def _serialize(self, instance, fields):
                         raise
                     else:
                         continue
+                if not required and not result:
+                    continue
+
                 if required or result is not None:
                     if call:
                         result = result()

tests/test_serializer.py

@@ -158,7 +158,7 @@ class ASerializer(Serializer):
 
         o = Obj(a=None)
         data = ASerializer(o).data
-        self.assertIsNone(data['a'])
+        self.assertNotIn('a', data)
 
         o = Obj(a='5')
         data = ASerializer(o).data
@@ -176,9 +176,6 @@ class ASerializer(DictSerializer):
             a = Field(required=False)
 
         data = ASerializer({'a': None}).data
-        self.assertIsNone(data['a'])
-
-        data = ASerializer({}).data
         self.assertNotIn('a', data)
 
         class ASerializer(DictSerializer):
@@ -196,10 +193,6 @@ class ASerializer(Serializer):
 
         o = Obj(a=None)
         data = ASerializer(o).data
-        self.assertIsNone(data['a'])
-
-        o = Obj()
-        data = ASerializer(o).data
         self.assertNotIn('a', data)
 
         class ASerializer(Serializer):