Pre test to automate the access token in Postman

Question

I tried to automate my postman test. In first test I should get access token to execute the API call. So I write pre test below. But I am getting 'There was an error in evaluating the Pre-request Script:Error: No data, empty input at 1:1 ^'. I tried commenting last section but it's not worked.

How should I automate this ?

const tokenUrl = 'https://xxxxxxxxxxxx/token';

const clientId = 'xxxxxxxxxxxxxxxx';
const clientSecret = 'xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx';

const getTokenRequest = {
  method: 'POST',
  url: tokenUrl,
  body: {
      mode: 'formdata',
      formdata: [
          { key: 'grant_type', value: 'Client Credentials' },
          { key: 'client_id', value: clientId },
          { key: 'client_secret', value: clientSecret }
      ]
  }
};

pm.sendRequest(getTokenRequest, (err, response) => {
const jsonResponse = response.json();
const newAccessToken = jsonResponse.access_token;

  pm.variables.set('access_token', newAccessToken);

  });