code: @DoesServiceRequest
      public FileOutputStream openWriteExisting() throws StorageException, URISyntaxException {
          return this
                  .openOutputStreamInternal(null /* length */, null /* accessCondition */, null /* options */, null /* opContext */);
      }
docs: Opens an output stream object to write data to the file. The file must already exist and any existing data may
  be overwritten.
  
  @return A {@link FileOutputStream} object used to write data to the file.
  
  @throws StorageException
  If a storage service error occurred.
  @throws URISyntaxException