KeyPath [..., ''] will be serialized to have a trailing comma, when deserializing it, we should
append back the empty string. Otherwise we will get inconsistent result with the KeyPath::Parse() method, causing assertions failure.
Differential Revision: https://phabricator.services.mozilla.com/D24724
--HG--
extra : moz-landing-system : lando
CreateMutableFile() doesn't allow empty name, we should check it before
further processing to avoid assertion failure.
Differential Revision: https://phabricator.services.mozilla.com/D23999
--HG--
extra : moz-landing-system : lando