static newEmpty(parentContext, forkLeavingPath) {
    return new ForkContext(
      parentContext.idGenerator,
      parentContext,
      (forkLeavingPath ? 2 : 1) * parentContext.count,
    );
  }
Creates an empty fork context preceded by a given context.
@param {ForkContext} parentContext The parent fork context.
@param {boolean} forkLeavingPath A flag which shows inside of `finally` block.
@returns {ForkContext} New fork context.