detect_noop doesn't work with null values

[clintongormley]

The detect_noop flag doesn't work if a field contains a null value:

PUT t/t/1
{
  "foo": "baz",
  "bar": "baz"
}

This update request always returns the same version:

POST t/t/1/_update
{
  "doc": {
    "foo": "baz",
    "bar": "baz"
  },
  "detect_noop": true
}

While this one always returns a new version:

POST t/t/1/_update
{
  "doc": {
    "foo": "baz",
    "bar": null
  },
  "detect_noop": true
}

[nik9000]

Eww. I can have a look in a bit.

[nik9000]

low hanging fruit indeed.

[ppf2]

@nik9000 @clintongormley Thx for the super quick turnaround on this 👍