Re: [PATCH 08/10] config tests: add "NULL" tests for *_get_value_multi()

> A less well known edge case in the config format is that keys can be
> value-less, a shorthand syntax for "true" boolean keys. I.e. these two
> are equivalent as far as "--type=bool" is concerned:
>
> 	[a]key
> 	[a]key = true
>
> But as far as our parser is concerned the values for these two are
> NULL, and "true". I.e. for a sequence like:
>
> 	[a]key=x
> 	[a]key
> 	[a]key=y
>
> We get a "struct string_list" with "string" members with ".string"
> values of:
>
> 	{ "x", NULL, "y" }
>
> This behavior goes back to the initial implementation of
> git_config_bool() in 17712991a59 (Add ".git/config" file parser,
> 2005-10-10).
>
> When the "t/t1308-config-set.sh" tests were added in [1] only one of
> the three "(NULL)" lines in "t/helper/test-config.c" had any test
> coverage. This change adds tests that stress the remaining two.