var customer = JSON.parse(responseBody);

if (customer.id === undefined) {
  // No customer was returned, so don't run the rest of the collection
  postman.setNextRequest(null);
}
else {
  // Save the customer ID to a Postman environment variable
  postman.setEnvironmentVariable("cust_id", customer.id);

  // The "Edit Customer" request uses the "cust_id" variable
  postman.setNextRequest('Edit Customer');
}