[geary] Application.ContactStore: Fix criticals from missing param nullable annotation

[Michael Gratton <mjog src gnome org>]

commit 64a7f8d3a90445899aca66220fcea8cab02bc1df
Author: Michael James Gratton <mike vee net>
Date:   Thu Jul 2 10:49:17 2020 +1000

    Application.ContactStore: Fix criticals from missing param nullable annotation

 src/client/application/application-contact-store.vala | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)
---
diff --git a/src/client/application/application-contact-store.vala 
b/src/client/application/application-contact-store.vala
index 16cbec4dd..981483fd3 100644
--- a/src/client/application/application-contact-store.vala
+++ b/src/client/application/application-contact-store.vala
@@ -188,7 +188,7 @@ public class Application.ContactStore : Geary.BaseObject {
 
     internal async Geary.Contact
         lookup_engine_contact(Geary.RFC822.MailboxAddress mailbox,
-                              GLib.Cancellable cancellable)
+                              GLib.Cancellable? cancellable)
         throws GLib.Error {
         string email_key = to_cache_key(mailbox.address);
         Geary.Contact contact = this.engine_address_cache.get_entry(email_key);
@@ -243,7 +243,7 @@ public class Application.ContactStore : Geary.BaseObject {
     }
 
     private async Folks.Individual? search_folks_by_email(string address,
-                                                          GLib.Cancellable cancellable)
+                                                          GLib.Cancellable? cancellable)
         throws GLib.Error {
         Folks.SearchView view = new Folks.SearchView(
             this.individuals,