[folks/wip/nielsdg/eds-error-assertion] eds: Add nullability to error contacts_complete_cb

[Niels De Graef <nielsdg src gnome org>]

commit 2827fded2470dd89f8840e2b5d4b56aa43959460
Author: Niels De Graef <nielsdegraef gmail com>
Date:   Mon Feb 3 23:41:14 2020 +0100

    eds: Add nullability to error contacts_complete_cb
    
    By not adding the nullable operator to the `GError` argument, Vala adds
    an precondition check that it shouldn't be null, which actually fails
    some tests.

 backends/eds/lib/edsf-persona-store.vala | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)
---
diff --git a/backends/eds/lib/edsf-persona-store.vala b/backends/eds/lib/edsf-persona-store.vala
index 2311277b..4afd9d22 100644
--- a/backends/eds/lib/edsf-persona-store.vala
+++ b/backends/eds/lib/edsf-persona-store.vala
@@ -2598,7 +2598,7 @@ public class Edsf.PersonaStore : Folks.PersonaStore
       return false;
     }
 
-  private void _contacts_complete_cb (Error err)
+  private void _contacts_complete_cb (Error? err)
     {
       /* Handle errors. We treat an error in the first _contacts_complete_cb()
        * callback as unrecoverable, since it's being reported from the address
@@ -2617,7 +2617,7 @@ public class Edsf.PersonaStore : Folks.PersonaStore
       this._idle_queue (() => { return this._contacts_complete_idle_cb (err); });
     }
 
-  private bool _contacts_complete_idle_cb (Error err)
+  private bool _contacts_complete_idle_cb (Error? err)
     {
       /* The initial query is complete, so signal that we've reached
        * quiescence (even if there was an error). */