### Please describe the problem.
git annex won't export subdirectories claiming they don't exist. `git rev-parse` however, returns hashes for said directories which then are accepted by `git annex export`.


### What steps will reproduce the problem?

[[!format sh """
$ git annex export master:folder --to exp
fatal: Path 'folder:' does not exist in 'master'
git-annex: unknown tree
$ git rev-parse master:folder
943218c141ab2a315b533fa9f92fe610916b5d1b
$ git annex export 943218c141ab2a315b533fa9f92fe610916b5d1b --to exp
export exp testfile2 
ok                          
(recording state in git...)
"""]]


### What version of git-annex are you using? On what operating system?
git-annex version: 6.20171026-g43d011a52 on Arch Linux

> [[fixed|done]] --[[Joey]]