Passing store: undefined leads to unexpected behavior

[Floriferous]

I wrote a cache with something like this:

let store = undefined;

if (someCondition) {
  store = new KeyvMongo();
}

const cache = new Keyv({ store })

When you try to clear the cache, the error is thrown from inside the clear() call. I would expect a default new Map() to be used when store is explicitly set to undefined.

Maybe an error should be thrown if the store is misconfigured?

[jaredwray]

@Floriferous - thanks so much for reporting this bug and I put a fix on #1339. It should be released in the next couple weeks.