Explicitly setting field with a default value to null sets it to default value instead of null

If you explicitly set a variable to null, and that variable has a default value like this query:

`myQuery(deleted: Boolean = false)`

and you call

`myQuery(deleted: null)`

environmeng.getArgument("deleted") still returns false, instead of null.

1) Is this a bug, or have I misunderstood the graphql spec?
2) Is there any way to make it return null instead?