fix empty array

Author: pinzon

.github/workflows/test.yml

@@ -42,7 +42,7 @@ jobs:
     runs-on: ubuntu-latest
     needs: generate-cdk-version-matrix
     strategy:
-      matrix: ${{fromJson(needs.generate-cdk-version-matrix.outputs.matrix || "{}")}}
+      matrix: ${{fromJson(needs.generate-cdk-version-matrix.outputs.matrix || '{}')}}
 
     steps:
       - uses: actions/checkout@v2