# HG changeset patch
# User Paul Boddie <paul@boddie.org.uk>
# Date 1423780806 -3600
# Node ID 22f373ae95b274d7c14774e310fbe166e913b2f1
# Parent  5825ecae680e33adfc20bb8efed434a27761cfbd
Return None from get_utc_datetime and get_datetime_item for nonexistent items.

diff -r 5825ecae680e -r 22f373ae95b2 imiptools/data.py
--- a/imiptools/data.py	Thu Feb 12 23:38:59 2015 +0100
+++ b/imiptools/data.py	Thu Feb 12 23:40:06 2015 +0100
@@ -249,12 +249,20 @@
     return get_values(d, name, False)
 
 def get_utc_datetime(d, name):
-    dt, attr = get_datetime_item(d, name)
-    return to_utc_datetime(dt)
+    t = get_datetime_item(d, name)
+    if not t:
+        return None
+    else:
+        dt, attr = t
+        return to_utc_datetime(dt)
 
 def get_datetime_item(d, name):
-    value, attr = get_item(d, name)
-    return get_datetime(value, attr), attr
+    t = get_item(d, name)
+    if not t:
+        return None
+    else:
+        value, attr = t
+        return get_datetime(value, attr), attr
 
 def get_addresses(values):
     return [address for name, address in email.utils.getaddresses(values)]