code: public String get(final String name, final String defaultv) {
      final String value = get(name);
      return value == null ? defaultv : value;
    }
docs: Returns the value of the given option, or a default value.
  @param name The name of the option to recognize (e.g. {@code --foo}).
  @param defaultv The default value to return if the option wasn't given.
  @throws IllegalArgumentException if this option wasn't registered with
  {@link #addOption}.
  @throws IllegalStateException if {@link #parse} wasn't called.