Issue with the returned value of data.keySet().toArray()[0]

[OKhalkov]

The function data.keySet().toArray()[0] returns an incorrect value of [0] instead of the expected value "devName"

var data = decodeToJson(payload);
var key = data.keySet().toArray()[0];
return {msg: data, metadata: metadata, key: data.keySet().toArray()[0]};

[OKhalkov]

the workaround is to take into parentheses