handle empty pkgs

Author: tmigot

.github/workflows/Breakage.yml

@@ -37,6 +37,9 @@ jobs:
           julia -e 'using Pkg; Pkg.Registry.add(RegistrySpec(url = "https://github.com/JuliaRegistries/General.git"))'
           julia --project=.breakage -e 'using Pkg; Pkg.update(); Pkg.instantiate()'
           pkgs=$(julia --project=.breakage .breakage/get_jso_users.jl ${{ env.pkg }})
+          if [[ -z "$pkgs" ]]; then
+            pkgs="[]"
+          fi
           vs='["latest", "stable"]'
           matrix=$(jq -cn --argjson deps "$pkgs" --argjson vers "$vs" '{pkg: $deps, pkgversion: $vers}')  # don't escape quotes like many posts suggest
           echo "matrix=$matrix" >> "$GITHUB_OUTPUT"