# HG changeset patch
# User Paul Boddie <paul@boddie.org.uk>
# Date 1509489980 -3600
# Node ID b4136058710415045a6257c8e5abca186646f760
# Parent  8978b422905b3c3e7dd7f6d69373fde12a0ecce3
Permit the generation of cancellation messages for all attendees.

diff -r 8978b422905b -r b41360587104 imiptools/client.py
--- a/imiptools/client.py	Tue Oct 31 23:45:34 2017 +0100
+++ b/imiptools/client.py	Tue Oct 31 23:46:20 2017 +0100
@@ -983,17 +983,19 @@
 
         """
         Prepare an event cancellation message involving the participants in the
-        'to_cancel' mapping.
+        'to_cancel' mapping or involving all participants if 'to_cancel' is not
+        specified or empty.
         """
 
-        if not to_cancel:
-            return None
+        obj = self.obj.copy()
 
-        obj = self.obj.copy()
-        obj["ATTENDEE"] = to_cancel.items()
+        if to_cancel:
+            obj["ATTENDEE"] = to_cancel.items()
+
+        recipients = self.get_recipients(obj)
 
         parts = [self.object_to_part("CANCEL", obj)]
-        return self.make_message(parts, to_cancel.keys())
+        return self.make_message(parts, recipients)
 
     def make_cancel_message_for_self(self, obj):