code: private CommandContainer<CI> getCommand(String commandName, String line) throws CommandNotFoundException {
          try {
              return registry.getCommand(commandName, line);
          }
          catch (CommandNotFoundException e) {
              // Lookup in aliases
              return registry.getCommandByAlias(commandName);
          }
      }
docs: try to return the command in the given registry if the given registry do
  not find the command, check if we have a internal registry and if its
  there.
  
  @param commandName command name
  @param line command line
  @return command
  @throws CommandNotFoundException