don't cache google docs tokens if they don't exist, fixes #4309
don't cache google docs tokens if they don't exist, fixes #4309

Change-Id: I8013760b88707d5c4fddec8563019d91a9360427
Reviewed-on: https://gerrit.instructure.com/3166
Reviewed-by: Zach Wily <9de8c4480303b5335cd2a33eefe814615ba3612a@instructure.com>
Tested-by: Hudson <dfb64870173313a9a7b56f814c8e3b33e268497a@instructure.com>

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