[gnome-builder] vala-pack: fix some g_warning()

[Christian Hergert <chergert src gnome org>]

commit 048b04369d48b9cd376905f4c898aeb9b940e98d
Author: Christian Hergert <chergert redhat com>
Date:   Thu Apr 25 23:56:30 2019 -0700

    vala-pack: fix some g_warning()

 src/plugins/vala-pack/lang-server/gnome-builder-vala.vala | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)
---
diff --git a/src/plugins/vala-pack/lang-server/gnome-builder-vala.vala 
b/src/plugins/vala-pack/lang-server/gnome-builder-vala.vala
index 17315c6eb..95c3c81f0 100644
--- a/src/plugins/vala-pack/lang-server/gnome-builder-vala.vala
+++ b/src/plugins/vala-pack/lang-server/gnome-builder-vala.vala
@@ -236,7 +236,11 @@ namespace Ide
 
                        string[] flags = {};
                        Jsonrpc.Message.parse (params, "flags", Jsonrpc.Message.GetStrv.create (ref flags));
-                       flags.length = (int) GLib.strv_length (flags);
+
+                       if (flags != null)
+                               flags.length = (int) GLib.strv_length (flags);
+                       else
+                               flags.length = 0;
 
                        GLib.Variant index_entries;
                        lock (index) {