is sharp(undefined, { raw: ... }) valid? if not, it would be handy to have it error.

[ericblade]

I had some issues where I was trying to do some processing with sharp, and was getting stuck inside a promise that never resolved or rejected. Turns out that I was accidentally passing in undefined variables as the first parameter to sharp(), and it took me quite a while to locate that as the culprit because there was no error or warning or anything.

[lovell]

Let's track this in #1768 as it's the same thing and benefits from a code sample.