Problem with handler script

Hi,

I am new to Mockaroo and I have set up a mock schema. I have added a request_header and would like to have the API request include the header every time the API is called, else an error message in the form of JSON is thrown. However, I am unsure if there are errors as I keep getting “null” instead of the error code and error messages.

Here is my handler script

schema "OTPVerify"
request_header 'clientID': 'test'
generate 1

if request_header 'clientID' == ''
  { resultCode: 'E0000', resultMessage: 'No Client ID.' }
end