disallow space in handle in register

Question

Hi , how to deny users to use space in username when register in site?

I add this code at qa-include/plugins/qa-filter-basic.php:51

if (preg_match('/\\s/', $handle)) {

    return qa_lang_sub('users/handle_has_bad', 'space');

}

but an error insert in error_log:

Question2Answer fatal error: Could not create a valid and unique handle from XXXXXX