Format error with string fields equal to null.

[sergey-gru]

When you export json resume from https://gitconnected.com/ the fiel durl is null. It's the same as "" - empty string.

#/basics/url : null

But validator marks this as an error.

If we try to read the json like text we wount be confused of the line:

{
  "basics": {
    "url": null,
  }
}

It seems like just unfilled field.

I propose to let all strings in the schema can be null. And be interpreted as ""