Issue 3726 DateTimeField not handling empty values

rest_framework/fields.py

@@ -1061,6 +1061,9 @@ class DateTimeField(Field):
         self.fail('invalid', format=humanized_format)
 
     def to_representation(self, value):
+        if not value:
+            return None
+
         output_format = getattr(self, 'format', api_settings.DATETIME_FORMAT)
 
         if output_format is None:

tests/test_fields.py

@@ -960,6 +960,8 @@ class TestDateTimeField(FieldValues):
     outputs = {
         datetime.datetime(2001, 1, 1, 13, 00): '2001-01-01T13:00:00',
         datetime.datetime(2001, 1, 1, 13, 00, tzinfo=timezone.UTC()): '2001-01-01T13:00:00Z'
+        None: None,
+        '': None,
     }
     field = serializers.DateTimeField(default_timezone=timezone.UTC())