code: @Override
      public String getValue(ParsedCommandLine args, boolean required) throws CommandFormatException {
          if(!required) {
              return null;
          }
          if(isPresent(args)) {
              return null;
          }
          throw new CommandFormatException("Required argument '" + fullName + "' is missing value.");
      }
docs: /* (non-Javadoc)
  @see org.jboss.as.cli.CommandArgument#getValue(org.jboss.as.cli.CommandContext)