Better check for duplicates

Author: AbitTheGray

.github/workflows/main.yml

@@ -22,6 +22,7 @@ jobs:
           else
             echo "No output file"
           fi
+
   file_to_file:
     runs-on: ubuntu-latest
     name: Test just copying the file

index.js

@@ -27,7 +27,7 @@ try
                 return;
 
             const filenameWithoutExtension = filename.substring(0, filename.length - ".json".length);
-            if(outputJson[filenameWithoutExtension] !== undefined)
+            if(!outputJson.hasOwnProperty(filenameWithoutExtension))
             {
                 core.error(filenameWithoutExtension + " is already defined (in " + inFile + ")");
                 return;