This is an attemps at fixing #1091 and #1203.

The issue

The documentation for implies is:

Given the key x is set, it is required that the key y is set.

But this check fails when the value of the key y is 0, false, or empty string.

When y value is false, we might want implies to continue failing though. I'd like to have your input on that, and I will adjust that PR accordingly.

The issue came from keyExists which, instead of always returning a boolean, could returned the value of the key. That value is later on used like so:

if (key && !value) {
  implyFail.push(` ${origKey} -> ${origValue}`);
}

Thus, that if resolved to true when value was 0, false or "".

The fix

Having keyExists always returning a boolean seems more robust. I used Object.hasOwnProperty to check for presence of the key instead.

Let me know if you think that keyExists should still return false when the value of the key is false.

Thanks :)