code: private Map<String, Object> handleParameterArg(final String arg, final Deque<String> args, final Argument argument) {
          final Map.Entry<String, String> entry = parse(arg, args);
          if (entry.getValue() == null) {
              throw new BuildException("Missing value for property " + entry.getKey());
          }
          return ImmutableMap.of(argument.property, argument.getValue(entry.getValue()));
      }
docs: Handler parameter argument