code: public RAMEntry touch(String name, long lastModifiedDate)
    {
      RAMEntry ramEntry = _directoryContent.get(name);
      if(ramEntry == null)
      {
        ramEntry = add(new RAMFile(_clock, name, new byte[0]));
      }
  
      ramEntry.touch(lastModifiedDate);
  
      return ramEntry;
    }
docs: Equivalent to 'touch' unix command: updates the last modified date to the value provided
  and if the entry does not create it, it creates an empty file!
  
  @param name
  @param lastModifiedDate
  @return the entry (either a new file or the entry that was modified)