from django.conf import settings
from django.db import models


class HashTag(models.Model):
    # The hash tag length can't be more than the body length minus the `#`
    text = models.CharField(max_length=139)

    def __str__(self):
        return self.text


class Message(models.Model):
    user = models.ForeignKey(settings.AUTH_USER_MODEL, related_name="messages")
    text = models.CharField(max_length=140)
    created_at = models.DateTimeField(auto_now_add=True)
    stars = models.ManyToManyField(
        settings.AUTH_USER_MODEL, related_name="starred_messages", blank=True)
    tagged_users = models.ManyToManyField(
        settings.AUTH_USER_MODEL, related_name="messages_tagged_in", blank=True)
    hash_tags = models.ManyToManyField(HashTag, blank=True)

    def __str__(self):
        return self.text

from django.conf import settings
from django.db import models


class HashTag(models.Model):
    # The hash tag length can't be more than the body length minus the `#`
    text = models.CharField(max_length=139)

    def __str__(self):
        return self.text


class Message(models.Model):
    user = models.ForeignKey(settings.AUTH_USER_MODEL, related_name="messages")
    text = models.CharField(max_length=140)
    created_at = models.DateTimeField(auto_now_add=True)
    stars = models.ManyToManyField(
        settings.AUTH_USER_MODEL, related_name="starred_messages")
    tagged_users = models.ManyToManyField(
        settings.AUTH_USER_MODEL, related_name="messages_tagged_in")
    hash_tags = models.ManyToManyField(HashTag)

    def __str__(self):
        return self.text
--- 
+++ 
@@ -15,10 +15,10 @@
     text = models.CharField(max_length=140)
     created_at = models.DateTimeField(auto_now_add=True)
     stars = models.ManyToManyField(
-        settings.AUTH_USER_MODEL, related_name="starred_messages")
+        settings.AUTH_USER_MODEL, related_name="starred_messages", blank=True)
     tagged_users = models.ManyToManyField(
-        settings.AUTH_USER_MODEL, related_name="messages_tagged_in")
-    hash_tags = models.ManyToManyField(HashTag)
+        settings.AUTH_USER_MODEL, related_name="messages_tagged_in", blank=True)
+    hash_tags = models.ManyToManyField(HashTag, blank=True)
 
     def __str__(self):
         return self.text
Add blank to allow no stars/tags in admin
