fix error when passing an undefined value

[kudarap]

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[kudarap]

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[e111077]

Heya, @javinc, thanks for the PR and sorry for the late review.

I see that this can run into issues if the key or the value is undefined, but can you provide a strong use case where this is necessary? An issue that I have with this is that you may have a url with bad params that fails silently.

Additionally, I think that an undefined value to an existent key is best to be kept out of the params as
key: undefined should not be represented as an empty string. Perhaps consider simply skipping the key/value encoding if the value is not defined.

[e111077]

see #207 null typically means that a value has specifically been set to be empty. undefined typically means that it was never set. I think that the best course of action here is that if it is undefined, that key / value pair should be skipped (e.g. { a: 'asdf', b: undefined } domain?a=asdf) and that a null value should be represented as either domain?key=, domain?key=null, or domain?key=%00.