Drop special-case support for missing keys

[zoul]

See #4 for longer discussion and rationale.

I’ve also added a commit that reformats the sources with Prettier – is my Prettier configuration wrong, or were the sources not completely formatted before? (We can drop this part if there’s something off with my Prettier.)

[tskj]

The thing with prettier is that they change the formatting with every version. I usually just accept the churn, but I'm open to locking it down in a config file in the project if you know how.

[tskj]

Thanks for putting this up!

I wonder if it's possible to give a better error message in the case that the key is actually missing and the decoder cannot handle undefined. As it stands now you get something like "undefined is not of type string, but of type undefined", which is kind of a weird error message. But I'm also not so sure if we can detect reliably (or explain in a good way to the user) that their decoder does not handle undefined and the key is missing (because it can throw for other reasons right?).

If not I will just merge this and take note of it as a potential improvement for later.

[zoul]

Prettier – if the formatting changes don’t annoy you, I’m fine with them. (I just wanted to make sure that this wasn’t some kind of formatting war between two incompatible configs :)

As for the error message, I don’t have a better solution now, I’m in favour of merging this and opening a new ticket to improve the error message later. Thank you!

[tskj]

Alright, I've made a mental note to improve it, so merge it is!

I tried formatting it locally on my machine, and it didn't seem to change, so I'm fairly sure this is just prettier having changed its mind.

[zoul]

(How soon will this make it to npm? I’ve got some work-in-progress code waiting for it, so I’d love to try it out :) But no pressure!)

[tskj]

Should be any minute. Without tests, deploying is very quick ;)