DateField to_representation can handle str and empty values. Fixes #2656, #2687.

rest_framework/fields.py

@@ -925,6 +925,9 @@ class DateField(Field):
         self.fail('invalid', format=humanized_format)
 
     def to_representation(self, value):
+        if not value:
+            return None
+
         if self.format is None:
             return value
 
@@ -938,7 +941,10 @@ class DateField(Field):
         )
 
         if self.format.lower() == ISO_8601:
+            if (isinstance(value, str)):
+                value = datetime.datetime.strptime(value, '%Y-%m-%d').date()
             return value.isoformat()
+
         return value.strftime(self.format)
 
 

tests/test_fields.py

@@ -726,7 +726,10 @@ class TestDateField(FieldValues):
         datetime.datetime(2001, 1, 1, 12, 00): ['Expected a date but got a datetime.'],
     }
     outputs = {
-        datetime.date(2001, 1, 1): '2001-01-01'
+        datetime.date(2001, 1, 1): '2001-01-01',
+        '2001-01-01': '2001-01-01',
+        None: None,
+        '': None,
     }
     field = serializers.DateField()