diff --git a/preferences/aes_field.py b/preferences/aes_field.py
index 27b026f7..81f8accc 100644
--- a/preferences/aes_field.py
+++ b/preferences/aes_field.py
@@ -33,6 +33,8 @@ def decrypt(key, s):
 
 class AESEncryptedField(models.CharField):
     def save_form_data(self, instance, data):
+        if value is None:
+            return value
         setattr(instance, self.name,
                 binascii.b2a_base64(encrypt(settings.AES_KEY, data)))
 
@@ -49,6 +51,8 @@ class AESEncryptedField(models.CharField):
                        binascii.a2b_base64(value)).decode('utf-8')
 
     def get_prep_value(self, value):
+        if value is None:
+            return value
         return binascii.b2a_base64(encrypt(
                     settings.AES_KEY,
                     value
diff --git a/preferences/migrations/0039_auto_20180115_0003.py b/preferences/migrations/0039_auto_20180115_0003.py
index da1b6631..3dbe2b4c 100644
--- a/preferences/migrations/0039_auto_20180115_0003.py
+++ b/preferences/migrations/0039_auto_20180115_0003.py
@@ -18,9 +18,4 @@ class Migration(migrations.Migration):
             name='payment_id',
             field=models.CharField(max_length=255, null=True),
         ),
-        migrations.AddField(
-            model_name='assooption',
-            name='payment_pass',
-            field=preferences.aes_field.AESEncryptedField(max_length=255, null=True),
-        ),
     ]
diff --git a/preferences/migrations/0040_auto_20180115_0010.py b/preferences/migrations/0040_auto_20180129_1745.py
similarity index 75%
rename from preferences/migrations/0040_auto_20180115_0010.py
rename to preferences/migrations/0040_auto_20180129_1745.py
index 407cb831..dc7800f4 100644
--- a/preferences/migrations/0040_auto_20180115_0010.py
+++ b/preferences/migrations/0040_auto_20180129_1745.py
@@ -1,5 +1,5 @@
 # -*- coding: utf-8 -*-
-# Generated by Django 1.10.7 on 2018-01-14 23:10
+# Generated by Django 1.10.7 on 2018-01-29 16:45
 from __future__ import unicode_literals
 
 from django.db import migrations, models
@@ -13,14 +13,14 @@ class Migration(migrations.Migration):
     ]
 
     operations = [
+        migrations.AddField(
+            model_name='assooption',
+            name='payment_pass',
+            field=preferences.aes_field.AESEncryptedField(blank=True, max_length=255, null=True),
+        ),
         migrations.AlterField(
             model_name='assooption',
             name='payment_id',
             field=models.CharField(default='', max_length=255),
         ),
-        migrations.AlterField(
-            model_name='assooption',
-            name='payment_pass',
-            field=preferences.aes_field.AESEncryptedField(default='', max_length=255),
-        ),
     ]
diff --git a/preferences/models.py b/preferences/models.py
index d4ef9645..4f1f388e 100644
--- a/preferences/models.py
+++ b/preferences/models.py
@@ -479,7 +479,8 @@ class AssoOption(models.Model):
     )
     payment_pass = AESEncryptedField(
         max_length=255,
-        default='',
+        null=True,
+        blank=True,
     )