Allow State.next_states to be blank so the admin doesn't barf

 - Legacy-Id: 5023

Author: OleLaursen

ietf/doc/models.py

@@ -27,7 +27,7 @@ class State(models.Model):
     desc = models.TextField(blank=True)
     order = models.IntegerField(default=0)
 
-    next_states = models.ManyToManyField('State', related_name="previous_states")
+    next_states = models.ManyToManyField('State', related_name="previous_states", blank=True)
 
     def __unicode__(self):
         return self.name