Support returning null for missing leaves in a path

[axsuul]

I'm not sure if this is supported already since I see that process_function_or_literal accepts a default value. But basically, if we have JSON that looks like this

{
  "data": [
     {
        "name" : "john",
        "gender" : "male"
    },
    {
        "name" : "ben"
    }
  ]
}

then the path data[*].gender will return (as expected)

["male"]

However, there are situations where a nil value is preferred to be returned instead if the leaf/key is missing. So perhaps something like

JsonPath.new('data[*].gender', default: nil).on(object)

will instead return

["male", nil]

This is already supported actually in the Java library: https://github.com/json-path/JsonPath

I don't mind submitting a pull request that supports this unless you know of a quick solution, thanks!

@Skarlso

[Skarlso]

Interesting stuff! Let me look into it. I'll tell you what's needed.

[axsuul]

@Skarlso Great!

[Skarlso]

Uh, it's a bit crappy, because default is not propagated properly anywhere. It's going to be a refactor with quite a size. @axsuul

[axsuul]

Alright, thanks for investigating. We can close this for now I guess and revisit in the future 👍

[Skarlso]

As you wish. :) I'm looking into ways of doing it nicely though. I'll say when I come up with one. :)

[Skarlso]

@axsuul Hey. @Seikitsu was so nice as to fix this issue apparently. Well done. :)