* @argv: (array length=argc) (inout) (allow-none): Address of the
* <parameter>argv</parameter> parameter of main(), or %NULL. Any options
* understood by GTK+ are stripped before return.
- * @parameter_string: a string which is displayed in
+ * @parameter_string: (allow-none): a string which is displayed in
* the first line of <option>--help</option> output, after
* <literal><replaceable>programname</replaceable> [OPTION...]</literal>
* @entries: (array zero-terminated=1): a %NULL-terminated array