Empty String Key is parsed as "undefined"

[boushley]

If I have a TOML file like:

"" = "foo bar"

this will be converted to {"undefined": "foo bar"}

This same issue exists at any level of nesting.

According to the TOML spec an empty quoted key is allowed: https://github.com/toml-lang/toml/blob/master/README.md#user-content-keys

It shows it as discouraged, but still shouldn't be parsed as "undefined"