Fix unknown contact display

src/pictures/models.py

@@ -16,7 +16,7 @@ class Contact(models.Model):
     display_name = models.CharField(max_length=250, blank=True)
 
     def __str__(self):
-        return self.display_name or self.phone_number
+        return self.display_name or str(self.phone_number)
 
 
 class Message(models.Model):

src/pictures/templates/pictures/messages-detail.html

@@ -13,7 +13,7 @@
 {% block content %}
     <div class="message">
         <div class="metadata">
-            <div class="name">De: {{ message.sender.display_name }}</div>
+            <div class="name">De: {{ message.sender }}</div>
             <div class="date">{{ message.received_at }}</div>
         </div>
         <div class="media">

src/pictures/templates/pictures/messages-list.html

@@ -17,7 +17,7 @@
             </div>
             <div class="content-block">
                 <div class="metadata">
-                    <div class="name">De: {{ message.sender.display_name }}</div>
+                    <div class="name">De: {{ message.sender }}</div>
                     <div class="date">{{ message.received_at }}</div>
                 </div>
                 <p class="text">{{ message.content | linebreaks }}</p>