function bbp_get_user_ids_from_nicenames( $user_nicenames = array() ) {

	// Default value
	$retval = array();

	// Only query if nicenames
	if ( ! empty( $user_nicenames ) ) {

		// Maybe explode by comma
		$user_nicenames = ( is_string( $user_nicenames ) && strstr( $user_nicenames, ',' ) )
			? explode( ',', $user_nicenames )
			: (array) $user_nicenames;

		// Sanitize each nicename in the array
		$user_nicenames = array_map( 'sanitize_title', $user_nicenames );

		// Get users
		$users = get_users( array(
			'nicename__in' => $user_nicenames
		) );

		// Pluck or empty
		if ( ! empty( $users ) ) {
			$retval = wp_list_pluck( $users, 'ID' );
		}
	}

	// Filter & return
	return (array) apply_filters( 'bbp_get_user_ids_from_nicenames', $retval, $user_nicenames );
}