[gnome-builder] flatpak: handle null when saving

[Christian Hergert <chergert src gnome org>]

commit 1d0360be5d7ebdf8d1712daab9fed084159e00d0
Author: Christian Hergert <chergert redhat com>
Date:   Sun Sep 6 08:57:16 2020 -0700

    flatpak: handle null when saving
    
    Fixes #1298

 src/plugins/flatpak/gbp-flatpak-manifest.c | 2 ++
 1 file changed, 2 insertions(+)
---
diff --git a/src/plugins/flatpak/gbp-flatpak-manifest.c b/src/plugins/flatpak/gbp-flatpak-manifest.c
index 07d8ff3e9..282103149 100644
--- a/src/plugins/flatpak/gbp-flatpak-manifest.c
+++ b/src/plugins/flatpak/gbp-flatpak-manifest.c
@@ -238,6 +238,8 @@ discover_environ (GbpFlatpakManifest *self,
         {
           if (JSON_NODE_HOLDS_VALUE (value))
             ide_environment_setenv (env, key, json_node_get_string (value));
+          else if (JSON_NODE_HOLDS_NULL (value))
+            ide_environment_setenv (env, key, "");
         }
     }