guzzle/guzzle — pull request #937 by mtdowling (2014-12-10 01:07:49+00:00)
Title: Setting a request option to null will ensure it is not set.

This commit makes it so that setting a request option to null will
ensure that the option is not set by the single request or as a result
of merging in default client settings (like being able to override proxy
on a one-off basis).