Port to new django version - not yet fully working

- location field makes problems

simpleforum/models.py

@@ -1,53 +1,43 @@
 from django.db import models
 from django.utils.translation import ugettext as _
 from django.contrib.auth.models import User
-
-
-class Message ( models.Model ):
-    
-    titel = models.CharField( max_length = 100, verbose_name = _("titel") )
-    text  = models.TextField( blank=False, verbose_name = _("text") )
-    
-    creation_time = models.DateTimeField( verbose_name=_("creation_time") )
-    
-    author = models.ForeignKey( User, verbose_name=_("Author") )
-    
-    
-    def __unicode__( self ):
-        return self.author.username + " : " + self.titel
-
-    
-
 from django.db.models.signals import post_save
 from django.dispatch import receiver
-
 from django.core.mail import EmailMultiAlternatives
-
 from musicians.models import Musician
-
 from django.template.loader import get_template
-
 from django.template import Context
 
+
+class Message(models.Model):
+    titel = models.CharField(max_length=100, verbose_name=_("titel"))
+    text = models.TextField(blank=False, verbose_name=_("text"))
+
+    creation_time = models.DateTimeField(verbose_name=_("creation_time"))
+    author = models.ForeignKey(User, verbose_name=_("Author"), on_delete=models.PROTECT)
+
+    def __unicode__(self):
+        return self.author.username + " : " + self.titel
+
+
 @receiver(post_save, sender=Message)
 def my_handler(sender, instance, created, **kwargs):
     if not created:
         return
-    
-    receivers = [  m.user.email  for m in Musician.objects.all()  ]
 
-    subject    = "Blechreiz Forum: " + instance.titel
+    receivers = [m.user.email for m in Musician.objects.all()]
+
+    subject = "Blechreiz Forum: " + instance.titel
     from_email = 'forum@blechreiz.com'
-    
-    c = {  'messages': Message.objects.all().order_by('-creation_time')[:10] }
-    
-    text_template = get_template( "simpleforum/mail.txt"  )
-    #html_template = get_template( "simpleforum/mail.html" )
-    
-    text_content = text_template.render( Context(c) )
-    #html_content = html_template.render( Context(c) )
-    
-    msg = EmailMultiAlternatives( subject, text_content, from_email, receivers )
-    #msg.attach_alternative( html_content, "text/html" )
+
+    c = {'messages': Message.objects.all().order_by('-creation_time')[:10]}
+
+    text_template = get_template("simpleforum/mail.txt")
+    # html_template = get_template( "simpleforum/mail.html" )
+
+    text_content = text_template.render(Context(c))
+    # html_content = html_template.render( Context(c) )
+
+    msg = EmailMultiAlternatives(subject, text_content, from_email, receivers)
+    # msg.attach_alternative( html_content, "text/html" )
     msg.send()
-