Do not attempt to change the status on an inbox message which doesn't exist. Fixes bug #12349.

docs/changelog/7.x.x.txt

@@ -12,6 +12,7 @@
  - fixed: Crud updateFromFormPost
  - fixed: encryptLogin and sslEnabled both need to be true
  - fixed: Cache's setByHTTP method returns content, even when it gets an error in the request.  This gives the SC asset fits.
+ - fixed #12349: Friends invitation error
 
 7.10.24
  - fixed #12318: asset error causes asset manager to fail

lib/WebGUI/Friends.pm

@@ -320,7 +320,10 @@ sub rejectAddRequest {
             status  => 'unread',
         });
     }
-    $inbox->getMessage($invite->{messageId})->setStatus('completed');
+    my $invitation = $inbox->getMessage($invite->{messageId});
+    if ($invitation) {
+        $invitation->setStatus('completed');
+    }
     $self->session->db->deleteRow("friendInvitations", "inviteId", $inviteId);
 }