Set nullable cause field of AuthorBalance

apps/payment/models.py

@@ -34,7 +34,7 @@ class AuthorBalance(models.Model):
     commission = models.DecimalField('Комиссия', max_digits=8, decimal_places=2, default=0)
     status = models.PositiveSmallIntegerField('Статус', choices=STATUS_CHOICES, default=0)
     payment = models.OneToOneField('Payment', on_delete=models.CASCADE, null=True, blank=True, verbose_name='Платёж')
-    cause = models.TextField('Причина отказа', default='')
+    cause = models.TextField('Причина отказа', null=True, blank=True)
 
     class Meta:
         verbose_name = 'Баланс'