code: public void register(String name, Command command) {
  		Preconditions.checkArgument(name != null && !name.isEmpty(), "Parameter 'name' must not be [" + name + "]");
  		Preconditions.checkArgument(command != null, "Parameter 'command' must not be [" + command + "]");
  		commands.put(name, command);
  	}
docs: Registers the specified command instance into the shell with the specified name.
  
  @param name Name of command.
  @param command Command to be registered.