Prevent case that login search string is empty

[linonetwo]

Might prevent a situation like https://github.com/solid/solid-cli/issues/8

[linonetwo]

Ok, I simply throw an error instead.

[linonetwo]

I'm going to add a test case, using jest.

[linonetwo]

const request = https.request(options);

isn't easy to mock using jest-fetch mock, would you mind I refactor it to node-fetch?

[jaxoncreed]

I think that should be fine @linonetwo