config: don't allow passing NULL as a value to set

Passing NULL is non-sensical. The error message leaves to be desired,
though, as it leaks internal implementation details. Catch it at the
`git_config_set_string` level and set an appropriate error message.

1 files changed, 14 insertions, 0 deletions

diff --git a/tests-clar/config/write.c b/tests-clar/config/write.c
index 1b665cd19..d70612a97 100644
--- a/tests-clar/config/write.c
+++ b/tests-clar/config/write.c
@@ -228,3 +228,17 @@ void test_config_write__add_value_at_file_with_no_clrf_at_the_end(void)
 
 	git_config_free(cfg);
 }
+
+void test_config_write__can_set_a_value_to_NULL(void)
+{
+    git_repository *repository;
+    git_config *config;
+
+    repository = cl_git_sandbox_init("testrepo.git");
+
+    cl_git_pass(git_repository_config(&config, repository));
+    cl_git_fail(git_config_set_string(config, "a.b.c", NULL));
+    git_config_free(config);
+
+    cl_git_sandbox_cleanup();
+}