Undefined index: wp_db_temp_dir

[chrispink]

This is not a consistent error and may be (as in I don't know if it is or isn't) attributable to a permissions error in the WP install but this error;

Undefined index: wp_db_temp_dir

is thrown by line 112

$requested_temp_dir = sanitize_text_field($_GET['wp_db_temp_dir']);

There appears to be a workaround replace line 112 with

if (isset($_GET['wp_db_temp_dir'])) {
    $requested_temp_dir = sanitize_text_field($_GET['wp_db_temp_dir']);
}

but I don't know if this truly 'works' in all situations.