Delete selector can't find keys with null values

[srounce]

Describe the bug
Delete doesn't work for paths with null values.

To Reproduce
Steps to reproduce the behavior:

> echo '{ "foo": null }' | dasel delete -r json 'foo'

< Error: could not access map index: property not found: foo

Expected behavior
I'd expect it to return {} instead I get the error above.

• OS: linux
• Version 2.3.4

[TomWright]

I've had a look and this is a tough problem to solve.

Related: golang/go#51649

I'm going to do some thinking and come back to this.

[TomWright]

Thanks for your patience on this.

I believe I have resolved this issue, see:

$ echo '{"foo":null}' | ./dasel -r json
{
  "foo": null
}
$ echo '{"foo":null}' | ./dasel -r json 'foo'
null
$ echo '{"foo":null}' | ./dasel delete -r json 'foo'
{}

The fix is on master and I'll create a release shortly.