When there was a key with no values in the query string,
there was a implicit conversion from string to list that
made the code compile but that messed up with the params.

That way, this query string `?hello` would be translated
into `?h&e&l&l&o`.

Signed-off-by: Albert Pastrana <albert.pastrana@gmail.com>

Can't remember where I got the numbers for the exponential
backoff test, but after several intermitent failures I just
checked what the min and max values should be and they are
slightly different from what I got.

With these new values the test should never fail.

Signed-off-by: Albert Pastrana <albert.pastrana@gmail.com>