Changed get to return empty string instead of null

[Tyxz]

empty string is better than null. Especially because there is no difference between empty cookie and null, but null might end up in an error imho. Also added a check method to see if a cookie already exists. Might be useful.

[Bigous]

Sounds fair to me!

[Bigous]

@carcamano Could you reveiw to accept the pull and publish a new minor version on npm?

[]'s

[carcamano]

Published. Thanks @Tyxz