Made a template filter more robust when given unexpected input.

 - Legacy-Id: 18417

Author: levkowetz

ietf/ipr/templatetags/ipr_filters.py

@@ -12,13 +12,16 @@
 def render_message_for_history(msg):
     """Format message for display in history.  Suppress the 'To' line for incoming responses
     """
-    if msg.to.startswith('ietf-ipr+'):
-        return format_html('Date: {}<br>From: {}<br>Subject: {}<br>Cc: {}<br><br>{}',
-            msg.time,msg.frm,msg.subject,msg.cc,msg.body)
+    from ietf.message.models import Message
+    if isinstance(msg, Message):
+        if msg.to.startswith('ietf-ipr+'):
+            return format_html('Date: {}<br>From: {}<br>Subject: {}<br>Cc: {}<br><br>{}',
+                msg.time,msg.frm,msg.subject,msg.cc,msg.body)
+        else:
+            return format_html('Date: {}<br>From: {}<br>To: {}<br>Subject: {}<br>Cc: {}<br><br>{}',
+                msg.time,msg.frm,msg.to,msg.subject,msg.cc,msg.body)
     else:
-        return format_html('Date: {}<br>From: {}<br>To: {}<br>Subject: {}<br>Cc: {}<br><br>{}',
-            msg.time,msg.frm,msg.to,msg.subject,msg.cc,msg.body)
-
+        return msg
 
 @register.filter
 def to_class_name(value):