How to pass or set null value in variable to post request

I’m posting HTTP request and JSR223 pre-processer to pass values like shown below,
Steps:

1. HTTP post request reading values from JSR223 pre-proccesser
2. Want to send null value for variable

JSR223 pre-processer :
vars.put("aptstatus","A")
vars.put("isccode",null)
I have used above way to pass value but in post request it is shown as

"status": "${aptstatus}",
"serviceCode": "${isccode}",

My requirement is to send null value in http post request.

Please help here how to set null value in variable.

Note: serviceCode is VARCHAR type

>Solution :

1. In the JSR223 PreProcessor:

   vars.put("isccode", 'null')
   

2. In the HTTP Request sampler:

   "status": "${aptstatus}", "serviceCode": ${isccode}
   

You will get:

"status": "A", "serviceCode": null

Demo:

More information on Groovy scripting in JMeter: Apache Groovy: What Is Groovy Used For?