'Get an appropriate "null" value for this field\'s type. This
is used internally when setting the field to None.'

def _none_value(self):

    if (self.out_type == int):
        return 0
    elif (self.out_type == float):
        return 0.0
    elif (self.out_type == bool):
        return False
    elif (self.out_type == six.text_type):
        return u''
