The Travis CI config runs the command:
git diff --name-only
49f6449ef4b81537c19b82329caaf60596c516c2...d0c822cded495409b68432fa10f9573417ca1fb7
Git fails with "fatal: Invalid symmetric difference expression (...)"
if it doesn't know one or both sha1.
The first problem is that 49f6449ef4b81537c19
I don't know if this is specific to my pull request but on PR #2558 I'm seeing:
fatal: Invalid symmetric difference expression
49f6449ef4b81537c19b82329caaf60596c516c2...7b634956246bc6112a16ba11ff9f721342e750e6
<>Only docs were updated, stopping build process.
The build is subsequently marked a
