cli: allow empty strings for notmuch insert --folder argument

Now that it's easy to add argument specific modifiers in opt
descriptions, add a new .allow_empty field to allow empty strings for
individual string arguments while retaining strict checks
elsewhere. Use this for notmuch insert --folder, where the empty
string means top level folder.

1 files changed, 1 insertions, 1 deletions

diff --git a/command-line-arguments.c b/command-line-arguments.c
index 1ff5aae5..db73ca5e 100644
--- a/command-line-arguments.c
+++ b/command-line-arguments.c
@@ -81,7 +81,7 @@ _process_string_arg (const notmuch_opt_desc_t *arg_desc, char next, const char *
 	fprintf (stderr, "Option \"%s\" needs a string argument.\n", arg_desc->name);
 	return false;
     }
-    if (arg_str[0] == '\0') {
+    if (arg_str[0] == '\0' && ! arg_desc->allow_empty) {
 	fprintf (stderr, "String argument for option \"%s\" must be non-empty.\n", arg_desc->name);
 	return false;
     }