@Nonnull
    default <T extends CommandExecutor> T registerCommand(@Nonnull T command, @Nonnull String... aliases) {
        return registerCommand(command, null, null, null, aliases);
    }
Registers a CommandExecutor with the server

@param command the command instance
@param aliases the command aliases
@param <T> the command executor class type
@return the command executor
helper/src/main/java/me/lucko/helper/plugin/HelperPlugin.java