how to send undefined value in postman?

Is there a way to send something like this in postman?

{
 "a": [undefined, {"b":"ball", "c":"cat"}]
}

Postman gives a red underline under undefined. If I use the pre-request script to pm.variables.set('undefinedVariable', undefined); and use this, then my code is giving this error

{
    "statusCode": 400,
    "error": "Bad Request",
    "message": "Invalid request payload JSON format"
}

>Solution :

It has nothing to do with node.js nor postman. undefined is not a valid json value even though it is valid in javascript. You may be able to use null instead

https://stackoverflow.com/a/14946821/6785908

• undefined is not a valid JSON value, even though it is valid in javascript.

  From the official JSON
  standard
  (ECMA-404, Section 5):

  A JSON value can be an object, array, number, string, true, false, or null.