# HG changeset patch
# User Paul Boddie <paul@boddie.org.uk>
# Date 1442614273 -7200
# Node ID 11ecf9db1d267e53b8be12196af1b824bcdab063
# Parent  0832ebaf5f61632e435ecefe627ca878f3372325
Handle undefined RDATE properties.

diff -r 0832ebaf5f61 -r 11ecf9db1d26 imiptools/data.py
--- a/imiptools/data.py	Fri Sep 18 23:45:56 2015 +0200
+++ b/imiptools/data.py	Sat Sep 19 00:11:13 2015 +0200
@@ -394,7 +394,7 @@
         previous RDATE properties and ignoring any RRULE properties.
         """
 
-        old_values = set(self.get_date_values("RDATE"))
+        old_values = set(self.get_date_values("RDATE") or [])
         new_rdates = []
 
         if self.has_key("RDATE"):
@@ -407,7 +407,7 @@
         if new_rdates:
             self["RDATE"] = new_rdates
 
-        return old_values != set(self.get_date_values("RDATE"))
+        return old_values != set(self.get_date_values("RDATE") or [])
 
     def correct_object(self, tzid, permitted_values):