[folks] Make BirthdayDetails.calendar_event_id nullable

[Philip Withnall <pwithnall src gnome org>]

commit 142f9b742847e907425b44070b46960dcb1b208f
Author: Philip Withnall <philip tecnocode co uk>
Date:   Sun Jul 10 19:52:03 2011 +0100

    Make BirthdayDetails.calendar_event_id nullable
    
    This includes expanding its documentation a little.

 NEWS                                  |    1 +
 backends/tracker/lib/trf-persona.vala |    2 +-
 folks/birthday-details.vala           |    6 ++++--
 3 files changed, 6 insertions(+), 3 deletions(-)
---
diff --git a/NEWS b/NEWS
index 7bcfe86..ea2f598 100644
--- a/NEWS
+++ b/NEWS
@@ -32,6 +32,7 @@ API changes:
 * Add a Persona.individual property
 * Add a Persona.writeable_properties property and implement it in all the
   Persona subclasses
+* Make BirthdayDetails.calendar_event_id nullable
 
 Overview of changes from libfolks 0.5.1 to libfolks 0.5.2
 =========================================================
diff --git a/backends/tracker/lib/trf-persona.vala b/backends/tracker/lib/trf-persona.vala
index 136f9a5..de06745 100644
--- a/backends/tracker/lib/trf-persona.vala
+++ b/backends/tracker/lib/trf-persona.vala
@@ -205,7 +205,7 @@ public class Trf.Persona : Folks.Persona,
   /**
    * { inheritDoc}
    */
-  public string calendar_event_id
+  public string? calendar_event_id
     {
       /* Unsupported */
       get { return null; }
diff --git a/folks/birthday-details.vala b/folks/birthday-details.vala
index 2303e0b..4ff2dc0 100644
--- a/folks/birthday-details.vala
+++ b/folks/birthday-details.vala
@@ -37,9 +37,11 @@ public interface Folks.BirthdayDetails : Object
   public abstract DateTime birthday { get; set; }
 
   /**
-   * The event id from the source calenar
+   * The event ID of the birthday event from the source calendar.
+   *
+   * If this is `null`, the birthday event is unknown.
    *
    * @since 0.4.0
    */
-  public abstract string calendar_event_id { get; set; }
+  public abstract string? calendar_event_id { get; set; }
 }