Clean Up Text

Remove strange chars from string. PHP

<?php
/**
 *
 * @author nebiros
 */

class App_Util
{
    public function cleanUpText( $input, $lowercase = true, $glue = "-" )
    {
        if ( true === empty( $input ) )
        {
            return null;
        }

        if ( true === $lowercase )
        {
            $input = strtolower( $input );
        }

        return preg_replace( "/[^a-zA-Z0-9_]/", "", preg_replace( "/\s+/", $glue, $input ) );
    }
}