Fixes for behavior with empty HTML fields.

rest_framework/fields.py

@@ -184,13 +184,11 @@ def __init__(self, read_only=False, write_only=False,
         self.style = {} if style is None else style
         self.allow_null = allow_null
 
-        if allow_null and self.default_empty_html 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
-
-        if default is not empty:
-            self.default_empty_html = default
+        if self.default_empty_html is not empty:
+            if not required:
+                self.default_empty_html = empty
+            elif default is not empty:
+                self.default_empty_html = default
 
         if validators is not None:
             self.validators = validators[:]
@@ -562,6 +560,11 @@ 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

@@ -215,25 +215,47 @@ class MockHTMLDict(dict):
         assert serializer.validated_data == {'archived': False}
 
 
+class MockHTMLDict(dict):
+    """
+    This class mocks up a dictionary like object, that behaves
+    as if it was returned for multipart or urlencoded data.
+    """
+    getlist = None
+
+
 class TestCharHTMLInput:
-    def setup(self):
+    def test_empty_html_checkbox(self):
         class TestSerializer(serializers.Serializer):
             message = serializers.CharField(default='happy')
-        self.Serializer = TestSerializer
 
-    def test_empty_html_checkbox(self):
-        """
-        HTML checkboxes do not send any value, but should be treated
-        as `False` by BooleanField.
-        """
-        # This class mocks up a dictionary like object, that behaves
-        # as if it was returned for multipart or urlencoded data.
-        class MockHTMLDict(dict):
-            getlist = None
-        serializer = self.Serializer(data=MockHTMLDict())
+        serializer = TestSerializer(data=MockHTMLDict())
         assert serializer.is_valid()
         assert serializer.validated_data == {'message': 'happy'}
 
+    def test_empty_html_checkbox_allow_null(self):
+        class TestSerializer(serializers.Serializer):
+            message = serializers.CharField(allow_null=True)
+
+        serializer = TestSerializer(data=MockHTMLDict())
+        assert serializer.is_valid()
+        assert serializer.validated_data == {'message': None}
+
+    def test_empty_html_checkbox_allow_null_allow_blank(self):
+        class TestSerializer(serializers.Serializer):
+            message = serializers.CharField(allow_null=True, allow_blank=True)
+
+        serializer = TestSerializer(data=MockHTMLDict({}))
+        assert serializer.is_valid()
+        assert serializer.validated_data == {'message': ''}
+
+    def test_empty_html_required_false(self):
+        class TestSerializer(serializers.Serializer):
+            message = serializers.CharField(required=False)
+
+        serializer = TestSerializer(data=MockHTMLDict())
+        assert serializer.is_valid()
+        assert serializer.validated_data == {}
+
 
 class TestCreateOnlyDefault:
     def setup(self):