Ensure formData value is not undefined

[fijimunkii]

PR Checklist:

• I have run npm test locally and all tests are passing.
• I have added/updated tests for any new behavior. (there is a test for null exception, there was none for undefined)
  
• If this is a significant change, an issue has already been created where the problem / solution was discussed: [ Ignore null and undefined values on processing formData #3063 ]
  

PR Description

One must be careful that all formData values are not undefined

An undefined value in form-data append will cause a confusing error:
TypeError: Cannot read property 'name' of undefined

Simple fix here is casting to empty string when value is undefined

To repro:

var formData = { woops: undefined };
var request = require('request');
request('https://github.com', { formData }, console.log)

Related PR to fix form-data form-data/form-data#417

[stale]

This issue has been automatically marked as stale because it has not had recent activity. It will be closed if no further activity occurs. Thank you for your contributions.