  
          self.validators = self.default_validators + validators
          self.default = default or self.default
  
          # Widgets are ony used for HTML forms.
          widget = widget or self.widget
          if isinstance(widget, type):
              widget = widget()
          self.widget = widget
 
</s> remove                  default=None):
 </s> add                  default=None, blank=None):
        self.blank = blank
  
          self.validators = self.default_validators + validators
          self.default = default or self.default
        self.blank = blank
  
          # Widgets are ony used for HTML forms.
          widget = widget or self.widget
          if isinstance(widget, type):
              widget = widget()
          self.widget = widget
keep keep add keep keep keep keep keep keep
 Merge fixes for 'blank=True' fields.  Fixes #324, Fixes #325

Thanks to @Roarster. 
rest_framework/fields.py