apply_filters( 'pre_user_nicename', string $user_nicename )

2355	 * Filters a user's nicename before the user is created or updated.2356	 *2357	 * @since 2.0.32358	 *2359	 * @param string $user_nicename The user's nicename.2360	 */2361	$user_nicename = apply_filters( 'pre_user_nicename', $user_nicename );2362 2363	// Check if the sanitized nicename is empty.2364	if ( empty( $user_nicename ) ) {2365		return new WP_Error( 'empty_user_nicename', __( 'Cannot create a user with an empty nicename.' ) );2366	} elseif ( mb_strlen( $user_nicename ) > 50 ) {2367		return new WP_Error( 'user_nicename_too_long', __( 'Nicename may not be longer than 50 characters.' ) );