only sign if key is available

.gitlab-ci.yml

@@ -91,7 +91,7 @@ package:
   script:
     - make -C gluon update GLUON_SITEDIR="$CI_PROJECT_DIR"
     - for branch in "stable" "beta" "nightly"; do make -C gluon manifest GLUON_BRANCH="$branch" GLUON_SITEDIR="$CI_PROJECT_DIR" V=1; done
-    - ./contrib/sign.sh <(echo "$GLUON_SIGN_KEY") output/images/sysupgrade/nightly.manifest
+    - test -z "$GLUON_SIGN_KEY" && ./contrib/sign.sh <(echo "$GLUON_SIGN_KEY") output/images/sysupgrade/nightly.manifest
   artifacts:
     paths:
       - gluon/output