I am attempting to leave a DECIMALFIELD blank. I would like my "if statement" to leave the field blank if it doesn't meet the criteria. My model is already set to blank=True, null=True.

def clean_xrate(self):
    xrate_date = self.cleaned_data.get(str("date"))
    currency = self.cleaned_data.get("currency")
    curr = currency
    if not xrate_date:
        raise ValidationError('Error')
    elif curr == 'USD':
        xrate = 'NULL' <---This doesn't work. ☹️
    else:
        prior_date_rate = cr.get_rate(curr, 'USD', xrate_date)
        xrate = "{0:.4f}".format(prior_date_rate)

    return xrate

Thanks in advance for your help!