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