Re: [PATCH 6/7] trailer: handle NULL value when parsing trailer-specific config

> When parsing the "key", "command", and "cmd" trailer config, we just
> make a copy of the value string.  If we see an implicit bool like:
> 
>   [trailer "foo"]
>   key
> 
> we'll segfault trying to copy a NULL pointer. We can fix this with the
> usual config_error_nonbool() check.
> 
> I split this out from the other vanilla cases, because at first glance
> it looks like a better fix here would be to move the NULL check out of
> the switch statement. But it would change the behavior of other keys
> like trailer.*.ifExists, where an implicit bool is interpreted as
> EXISTS_DEFAULT.
> 
> Signed-off-by: Jeff King <peff@peff.net>
> ---
>  trailer.c | 6 ++++++
>  1 file changed, 6 insertions(+)
> 
> diff --git a/trailer.c b/trailer.c
> index b0e2ec224a..e4b08ed267 100644
> --- a/trailer.c
> +++ b/trailer.c
> @@ -553,16 +553,22 @@ static int git_trailer_config(const char *conf_key, const char *value,
>  	case TRAILER_KEY:
>  		if (conf->key)
>  			warning(_("more than one %s"), conf_key);
> +		if (!value)
> +			return config_error_nonbool(conf_key);
>  		conf->key = xstrdup(value);
>  		break;
>  	case TRAILER_COMMAND:
>  		if (conf->command)
>  			warning(_("more than one %s"), conf_key);
> +		if (!value)
> +			return config_error_nonbool(conf_key);
>  		conf->command = xstrdup(value);
>  		break;
>  	case TRAILER_CMD:
>  		if (conf->cmd)
>  			warning(_("more than one %s"), conf_key);
> +		if (!value)
> +			return config_error_nonbool(conf_key);
>  		conf->cmd = xstrdup(value);
>  		break;
>  	case TRAILER_WHERE: