this is an issue with Java and has nothing to do with the node. Your call to URLDecoder.decode can potentially throw an exception of type UnsupportedEncodingException (source: https://docs.oracle.com/javase/6/docs/api/java/net/URLDecoder.html#decode)
The way you can fix this is as follows: Surround your call to .decode() with a try{} catch() {} clause that catches UnsupportedEncodingException. If you always provide "UTF-8" as the second parameter, your catch-clause can contain no action because the error will never happen.
Or, to say it in code:
try {
return URLDecoder.decode($variable, "UTF-8");
} catch( UnsupportedEncodingException e ) {
//do nothing, because this will never happen as long as the provided encoding is "UTF-8"