Apparently outputs must be strings...

Author: TheBusyBiscuit

README.md

@@ -16,7 +16,7 @@ You can use the built-in ${{ secrets.GITHUB_TOKEN }} variable for this.
 ## Outputs
 
 ### `issues`
-The output of this is an Array of numbers, corresponding to the issue numbers that were closed via commits.
+The output of this is a JSON Array of numbers, corresponding to the issue numbers that were closed via commits.
 
 ## Example usages
 

src/index.js

@@ -46,7 +46,7 @@ async function run() {
 		}
 	}
 
-	core.setOutput("issues", issues);
+	core.setOutput("issues", JSON.stringify(issues));
 }
 
 try {