static updateGroupOptions(parentOptions, newOptions, groupList) {
    if (groupList === undefined) return; // No groups, nothing to do

    const group = parentOptions.group;

    // paranoia: the selected group is already merged into node options, check.
    if (
      newOptions !== undefined &&
      newOptions.group !== undefined &&
      group !== newOptions.group
    ) {
      throw new Error(
        "updateGroupOptions: group values in options don't match."
      );
    }

    const hasGroup =
      typeof group === "number" || (typeof group === "string" && group != "");
    if (!hasGroup) return; // current node has no group, no need to merge

    const groupObj = groupList.get(group);

    if (groupObj.opacity !== undefined && newOptions.opacity === undefined) {
      if (!Node.checkOpacity(groupObj.opacity)) {
        console.error(
          "Invalid option for node opacity. Value must be between 0 and 1, found: " +
            groupObj.opacity
        );
        groupObj.opacity = undefined;
      }
    }

    // Skip any new option to avoid them being overridden by the group options.
    const skipProperties = Object.getOwnPropertyNames(newOptions).filter(
      (p) => newOptions[p] != null
    );
    // Always skip merging group font options into parent; these are required to be distinct for labels
    skipProperties.push("font");
    selectiveNotDeepExtend(skipProperties, parentOptions, groupObj);

    // the color object needs to be completely defined.
    // Since groups can partially overwrite the colors, we parse it again, just in case.
    parentOptions.color = parseColor(parentOptions.color);
  }
Copy group option values into the node options.

The group options override the global node options, so the copy of group options
must happen *after* the global node options have been set.

This method must also be called also if the global node options have changed and the group options did not.
@param {object} parentOptions
@param {object} newOptions  new values for the options, currently only passed in for check
@param {object} groupList