[PATCH 4/5] config: return an empty list, not NULL

["Derrick Stolee via GitGitGadget" <gitgitgadget@gmail.com>]

From: Derrick Stolee <derrickstolee@github.com>

For the multi-valued config API methods, Git previously returned a NULL
list instead of an empty list. Previous changes adjusted all callers to
instead expect an empty, non-NULL list, making this a safe change.

The next change will remove the NULL checks from all callers.

Signed-off-by: Derrick Stolee <derrickstolee@github.com>
---
 config.c | 3 ++-
 config.h | 6 +++---
 2 files changed, 5 insertions(+), 4 deletions(-)

diff --git a/config.c b/config.c
index 0c41606c7d4..2d4ca1ae6dc 100644
--- a/config.c
+++ b/config.c
@@ -2415,8 +2415,9 @@ int git_configset_get_value(struct config_set *cs, const char *key, const char *
 
 const struct string_list *git_configset_get_value_multi(struct config_set *cs, const char *key)
 {
+	static struct string_list empty_list = STRING_LIST_INIT_NODUP;
 	struct config_set_element *e = configset_find_element(cs, key);
-	return e ? &e->value_list : NULL;
+	return e ? &e->value_list : &empty_list;
 }
 
 int git_configset_get_string(struct config_set *cs, const char *key, char **dest)
diff --git a/config.h b/config.h
index ca994d77147..9897b97c0b9 100644
--- a/config.h
+++ b/config.h
@@ -458,7 +458,7 @@ int git_configset_add_parameters(struct config_set *cs);
 /**
  * Finds and returns the value list, sorted in order of increasing priority
  * for the configuration variable `key` and config set `cs`. When the
- * configuration variable `key` is not found, returns NULL. The caller
+ * configuration variable `key` is not found, returns an empty list. The caller
  * should not free or modify the returned pointer, as it is owned by the cache.
  */
 const struct string_list *git_configset_get_value_multi(struct config_set *cs, const char *key);
@@ -543,8 +543,8 @@ int git_config_get_value(const char *key, const char **value);
 /**
  * Finds and returns the value list, sorted in order of increasing priority
  * for the configuration variable `key`. When the configuration variable
- * `key` is not found, returns NULL. The caller should not free or modify
- * the returned pointer, as it is owned by the cache.
+ * `key` is not found, returns an empty list. The caller should not free or
+ * modify the returned pointer, as it is owned by the cache.
  */
 const struct string_list *git_config_get_value_multi(const char *key);
 
-- 
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