Allow blank choices to render. Closes #2071.

rest_framework/fields.py

@@ -947,6 +947,8 @@ class ChoiceField(Field):
             self.fail('invalid_choice', input=data)
 
     def to_representation(self, value):
+        if value in ('', None):
+            return value
         return self.choice_strings_to_values[six.text_type(value)]
 
 

tests/test_fields.py

@@ -793,7 +793,8 @@ class TestChoiceField(FieldValues):
         'amazing': ['`amazing` is not a valid choice.']
     }
     outputs = {
-        'good': 'good'
+        'good': 'good',
+        '': ''
     }
     field = serializers.ChoiceField(
         choices=[