Support allow_blank=False with trim_whitespace=True.

rest_framework/fields.py

@@ -580,7 +580,7 @@ class CharField(Field):
         # Test for the empty string here so that it does not get validated,
         # and so that subclasses do not need to handle it explicitly
         # inside the `to_internal_value()` method.
-        if data == '':
+        if data == '' or (self.trim_whitespace and six.text_type(data).strip() == ''):
             if not self.allow_blank:
                 self.fail('blank')
             return ''

tests/test_fields.py

@@ -461,6 +461,13 @@ class TestCharField(FieldValues):
         field = serializers.CharField(trim_whitespace=False)
         assert field.to_internal_value(' abc ') == ' abc '
 
+    def test_disallow_blank_with_trim_whitespace(self):
+        field = serializers.CharField(allow_blank=False, trim_whitespace=True)
+
+        with pytest.raises(serializers.ValidationError) as exc_info:
+            field.run_validation('   ')
+        assert exc_info.value.detail == ['This field may not be blank.']
+
 
 class TestEmailField(FieldValues):
     """