1.1 --- a/imiptools/client.py	Fri Sep 11 13:40:39 2015 +0200
     1.2 +++ b/imiptools/client.py	Fri Sep 11 15:49:33 2015 +0200
     1.3 @@ -268,6 +268,12 @@
     1.4          self.sequence = obj and self.obj.get_value("SEQUENCE")
     1.5          self.dtstamp = obj and self.obj.get_value("DTSTAMP")
     1.6  
     1.7 +    def is_usable(self):
     1.8 +
     1.9 +        "Return whether the current object is usable."
    1.10 +
    1.11 +        return True
    1.12 +
    1.13      # Object update methods.
    1.14  
    1.15      def update_recurrenceid(self):
    1.16 @@ -286,7 +292,7 @@
    1.17  
    1.18          dtstamp = self.obj.get_utc_datetime("DTSTAMP")
    1.19          utcnow = to_timezone(datetime.utcnow(), "UTC")
    1.20 -        self.dtstamp = format_datetime(dtstamp > utcnow and dtstamp or utcnow)
    1.21 +        self.dtstamp = format_datetime(dtstamp and dtstamp > utcnow and dtstamp or utcnow)
    1.22          self.obj["DTSTAMP"] = [(self.dtstamp, {})]
    1.23  
    1.24      def set_sequence(self, increment=False):

     2.1 --- a/imiptools/content.py	Fri Sep 11 13:40:39 2015 +0200
     2.2 +++ b/imiptools/content.py	Fri Sep 11 15:49:33 2015 +0200
     2.3 @@ -69,7 +69,8 @@
     2.4                  # Dispatch to a handler and obtain any response.
     2.5  
     2.6                  handler.set_object(Object({name : item}))
     2.7 -                methods[method](handler)()
     2.8 +                if handler.is_usable():
     2.9 +                    methods[method](handler)()
    2.10  
    2.11  # Handler registry.
    2.12  

     3.1 --- a/imiptools/data.py	Fri Sep 11 13:40:39 2015 +0200
     3.2 +++ b/imiptools/data.py	Fri Sep 11 15:49:33 2015 +0200
     3.3 @@ -648,6 +648,7 @@
     3.4      """
     3.5      Return the value provided by 'd' for 'name' as a datetime in the UTC zone
     3.6      or as a date, converting any date to a datetime if 'date_tzid' is specified.
     3.7 +    If no datetime or date is available, None is returned.
     3.8      """
     3.9  
    3.10      t = get_datetime_item(d, name)
    3.11 @@ -655,7 +656,7 @@
    3.12          return None
    3.13      else:
    3.14          dt, attr = t
    3.15 -        return to_utc_datetime(dt, date_tzid)
    3.16 +        return dt is not None and to_utc_datetime(dt, date_tzid) or None
    3.17  
    3.18  def get_datetime_item(d, name):
    3.19  

     4.1 --- a/imiptools/handlers/common.py	Fri Sep 11 13:40:39 2015 +0200
     4.2 +++ b/imiptools/handlers/common.py	Fri Sep 11 15:49:33 2015 +0200
     4.3 @@ -70,6 +70,12 @@
     4.4  
     4.5      "Common outgoing message handling functionality mix-in."
     4.6  
     4.7 +    def is_usable(self):
     4.8 +
     4.9 +        "Return whether the current object is usable."
    4.10 +
    4.11 +        return self.obj and self.obj.get_value("DTSTART") 
    4.12 +
    4.13      def update_event_in_freebusy(self, for_organiser=True):
    4.14  
    4.15          """