update Sliver admin
diff --git a/plstackapi/core/models/user.py b/plstackapi/core/models/user.py
index c21601c..30bd2a9 100644
--- a/plstackapi/core/models/user.py
+++ b/plstackapi/core/models/user.py
@@ -9,7 +9,7 @@
 # Create your models here.
 
 class User(PlCoreBase):
-    user_id = models.CharField(max_length=256, unique=True, blank=True)
+    user_id = models.CharField(max_length=256, unique=True)
     firstname = models.CharField(help_text="person's given name", max_length=200)
     lastname = models.CharField(help_text="person's surname", max_length=200)
     email = models.EmailField(help_text="e-mail address", null=True)