Confusion around variables with default values and `null` value

[cjoudrey]

While working on an issue in graphql-ruby, I needed clarity on the expected behaviour of variables with default values and null value in the following example:

Query

query ($id: ID = 4) {
  film(filmID: $id) {
    title
  }
}

Variables

{
  "id": null
}

In graphql-js, null takes precedence over the default value of $id and the film resolver receives filmID: null.

The spec suggests the following algorithm for dealing with this case:

However, I got a bit confused when I read this:

It might just be me, but I got confused with "represent the lack of a value" and "if value does not exist".

Is "represent the lack of a value" misleading?

/cc @leebyron re: #83
/cc @rmosolgo @xuorig what we were talking about

[leebyron]

I agree this can be confusing. The explicit value null is semantically different from no value being provided. I attempted to clear this up in #418 however please open new issues if there are still sections you find confusing!