Better behavior with null and '' for blank HTML fields.

rest_framework/fields.py

@@ -273,7 +273,11 @@ def get_value(self, dictionary):
                     return empty
                 return self.default_empty_html
             ret = dictionary[self.field_name]
-            return self.default_empty_html if (ret == '') else ret
+            if ret == '' and self.allow_null:
+                # If the field is blank, and null is a valid value then
+                # determine if we should use null instead.
+                return '' if getattr(self, 'allow_blank', False) else None
+            return ret
         return dictionary.get(self.field_name, empty)
 
     def get_attribute(self, instance):
@@ -545,8 +549,6 @@ class CharField(Field):
         'min_length': _('Ensure this field has at least {min_length} characters.')
     }
     initial = ''
-    coerce_blank_to_null = False
-    default_empty_html = ''
 
     def __init__(self, **kwargs):
         self.allow_blank = kwargs.pop('allow_blank', False)
@@ -560,11 +562,6 @@ def __init__(self, **kwargs):
             message = self.error_messages['min_length'].format(min_length=min_length)
             self.validators.append(MinLengthValidator(min_length, message=message))
 
-        if self.allow_null and (not self.allow_blank) and (self.default is empty):
-            # HTML input cannot represent `None` values, so we need to
-            # forcibly coerce empty HTML values to `None` if `allow_null=True`.
-            self.default_empty_html = None
-
     def run_validation(self, data=empty):
         # Test for the empty string here so that it does not get validated,
         # and so that subclasses do not need to handle it explicitly

tests/test_fields.py

@@ -223,32 +223,40 @@ class MockHTMLDict(dict):
     getlist = None
 
 
-class TestCharHTMLInput:
-    def test_empty_html_checkbox(self):
+class TestHTMLInput:
+    def test_empty_html_charfield(self):
         class TestSerializer(serializers.Serializer):
             message = serializers.CharField(default='happy')
 
         serializer = TestSerializer(data=MockHTMLDict())
         assert serializer.is_valid()
         assert serializer.validated_data == {'message': 'happy'}
 
-    def test_empty_html_checkbox_allow_null(self):
+    def test_empty_html_charfield_allow_null(self):
         class TestSerializer(serializers.Serializer):
             message = serializers.CharField(allow_null=True)
 
-        serializer = TestSerializer(data=MockHTMLDict())
+        serializer = TestSerializer(data=MockHTMLDict({'message': ''}))
         assert serializer.is_valid()
         assert serializer.validated_data == {'message': None}
 
-    def test_empty_html_checkbox_allow_null_allow_blank(self):
+    def test_empty_html_datefield_allow_null(self):
+        class TestSerializer(serializers.Serializer):
+            expiry = serializers.DateField(allow_null=True)
+
+        serializer = TestSerializer(data=MockHTMLDict({'expiry': ''}))
+        assert serializer.is_valid()
+        assert serializer.validated_data == {'expiry': None}
+
+    def test_empty_html_charfield_allow_null_allow_blank(self):
         class TestSerializer(serializers.Serializer):
             message = serializers.CharField(allow_null=True, allow_blank=True)
 
-        serializer = TestSerializer(data=MockHTMLDict({}))
+        serializer = TestSerializer(data=MockHTMLDict({'message': ''}))
         assert serializer.is_valid()
         assert serializer.validated_data == {'message': ''}
 
-    def test_empty_html_required_false(self):
+    def test_empty_html_charfield_required_false(self):
         class TestSerializer(serializers.Serializer):
             message = serializers.CharField(required=False)