Ohh, there could be some other issue.
Array.length can never give you null, if it’s not an array but an object then it will give you an undefined.
I think the x is actually an object here which already has a property length with a value null
Can you write console.log(x, Array.isArray(x)); and open Postman console and show the result after you send the request?
Feel free to retract any sensitive information.