bp_core_get_userid_from_nicename( string $user_nicename = '' )

function bp_core_get_userid_from_nicename( $user_nicename = '' ) {
	if ( empty( $user_nicename ) ) {
		return false;
	}

	$user = get_user_by( 'slug', $user_nicename );

	/**
	 * Filters the user ID based on user_nicename.
	 *
	 * @since BuddyPress 1.2.3
	 *
	 * @param int|null $value         ID of the user or null.
	 * @param string   $user_nicename User nicename to check.
	 */
	return apply_filters( 'bp_core_get_userid_from_nicename', ! empty( $user->ID ) ? $user->ID : NULL, $user_nicename );
}