Currently, if get_git_head_revision() doesn't define GIT_SHA1 (which it
doesn't in some cases) it's possible to end up with the following error:
CMake Error at CMakeLists.txt:69 (if):
if given arguments:
"STREQUAL" "GITDIR-NOTFOUND"
Unknown arguments specified
Fix this by making sure both left and right hand arguments to STREQUAL
are always strings, even if GIT_SHA1 is undefined.
Signed-off-by: Kyle Fazzari <kyle@canonical.com>
