RFC config API: return empty list, not NULL

This work changes the behavior of asking for a multi-valued config key to return an empty list instead of a NULL value. This simplifies the handling of the result and is safer for development in the future.

This is based on v4 of my unregister series [1]

[1]
https://lore.kernel.org/git/[email protected]/

This idea came about due to a bug in the git maintenance unregister work where the result from git_config_get_value_multi() was sent directly to for_each_string_list_item() without checking for a NULL value first.

I'm sending this as an RFC mostly because I'm not 100% sure this shift is worth the refactoring pain and effort. I personally think getting an empty list is a safer choice, but I can also understand if someone has a different opinion.

Thanks, -Stolee

Derrick Stolee (5):
config: relax requirements on multi-value return *: relax git_configset_get_value_multi result
config: add BUG() statement instead of possible segfault
config: return an empty list, not NULL
*: expect a non-NULL list of config values

 builtin/for-each-repo.c     |  8 --------
 builtin/gc.c                | 20 ++++++++------------
 builtin/log.c               | 10 ++++------
 builtin/pack-objects.c      |  3 ---
 builtin/repack.c            | 13 +++++--------
 builtin/submodule--helper.c |  4 ++--
 config.c                    | 15 ++++++++++-----
 config.h                    |  6 +++---
 pack-bitmap.c               |  3 ---
 submodule.c                 |  2 +-
 t/helper/test-config.c      |  4 ++--
 versioncmp.c                |  8 ++++----
 12 files changed, 39 insertions(+), 57 deletions(-)

base-commit: 73a262cdca46a45aeeda6f47ea3357aaeb937e7b
Published-As: https://github.com/gitgitgadget/git/releases/tag/pr-1369%2Fderrickstolee%2Fconfig-empty-list-v1
Fetch-It-Via: git fetch https://github.com/gitgitgadget/git pr-1369/derrickstolee/config-empty-list-v1
Pull-Request: https://github.com/gitgitgadget/git/pull/1369

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