Fix isNullish to not consider an empty string as Null.

[augustoroman]

An empty string is still a perfectly valid string, in both situations:
(1) An empty string is a valid string argument to a handler.
(2) An empty string is a valid non-null result from a handler.

I also removed the unused and unnecessary PrivateName value from the
NonNull struct -- it served no purpose and screwed up tests when isNullish
was fixed.

See also #107

[franklinkim]

+1

[Matthias247]

@sogko Is there any reason not to merge this apart from the need to rebase? It's currently a little bit annoying that no empty strings are supported.

[kyteague]

Like @Matthias247 said, any reason this major bug fix has not been merged?

[rogchap]

Would love to see this fix land.
Maybe we need more people to be core contributors @sogko @chris-ramon ??
Not much activity for a while on this repo.

[solher]

Agreed. Any news on this one? @sogko

[edast]

+1
can this be merged soon?

[martynasb]

+1 Please land this

[bbuck]

@sogko @chris-ramon I think we should cleanup/update this PR (or create a fresh one) and get this change rolling along. The behavior can definitely be confusing, but it's not a small change (as far as who it reaches) as it's a breaking API change if people are depending on the current behavior. But after discussion in #183 I'm convinced that "" should not be considered as null unless we should also consider other zero values as null as well.

[chris-ramon]

closing this one in favor of #228 — thanks a lot @augustoroman 👍