Difficult to understand note in GQL spec

https://facebook.github.io/graphql/June2018/#sec-Null-Value

"The same two methods of representing the lack of a value are possible via variables by either providing the a variable value as null and not providing a variable value at all."

I'd be happy to update this with a PR however I'm not sure what to replace it with.

1. "the a variable" looks like a grammar mistake.
2. "[V]ariable" should be called out more explicitly since the paragraph right above speaks of arguments and the two are easily confused for one another.
3. I'm not entirely sure what this is trying to state. Does it mean, "Using a _Variable_ of value `null` and not providing a _Variable_ at all are equivalent"? Which would mean `null` is the same as no value existing for the argument? Doesn't this contradict "The first has explicitly provided null to the argument “arg”, while the second has implicitly not provided a value to the argument “arg”. These two forms may be interpreted differently."?

Once 3 is clarified I'd be happy to open a PR.