Writing Custom Thingworx Service 400 - 500 Level Error Return Code

I want to do something like this - 

try{

if(someError)

   throw someErrorException()

}catch someErrorException{

result.message  = "someError happened"

}

Expected output in postman if the someError condition is true -

Status Code = 500 & response message = someError happened"

Instead of this, I am able to get it into status code 500 by forcefully writing erroneous code within the if statement but I am not able to set the error message. Its the standard error message which comes - "XYZ check scriptLog"