Merge branch 'maint'

* maint: (35 commits)
config.c: guard config parser from value=NULL
builtin-log.c: guard config parser from value=NULL
imap-send.c: guard config parser from value=NULL
wt-status.c: guard config parser from value=NULL
setup.c: guard config parser from value=NULL
remote.c: guard config parser from value=NULL
merge-recursive.c: guard config parser from value=NULL
http.c: guard config parser from value=NULL
help.c: guard config parser from value=NULL
git.c: guard config parser from value=NULL
diff.c: guard config parser from value=NULL
convert.c: guard config parser from value=NULL
connect.c: guard config parser from value=NULL
builtin-tag.c: guard config parser from value=NULL
builtin-show-branch.c: guard config parser from value=NULL
builtin-reflog.c: guard config parser from value=NULL
builtin-log.c: guard config parser from value=NULL
builtin-config.c: guard config parser from value=NULL
builtin-commit.c: guard config parser from value=NULL
builtin-branch.c: guard config parser from value=NULL
...

diff --cc Documentation/config.txt
Simple merge

diff --cc builtin-pack-objects.c
Simple merge

diff --cc config.c
Simple merge

diff --cc t/t1300-repo-config.sh
Simple merge