code: @DoesServiceRequest
      public FileOutputStream openWriteExisting(AccessCondition accessCondition, FileRequestOptions options,
              OperationContext opContext) throws StorageException, URISyntaxException {
          return this.openOutputStreamInternal(null /* length */, accessCondition, options, opContext);
      }
docs: Opens an output stream object to write data to the file, using specified request options and
  operation context. The file must already exist and any existing data may be overwritten.
  
  @param accessCondition
  An {@link AccessCondition} object which represents the access conditions for the file.
  @param options
  A {@link FileRequestOptions} object that specifies any additional options for the request. Specifying
  <code>null</code> will use the default request options from the associated service client (
  {@link CloudFileClient}).
  @param opContext
  An {@link OperationContext} object which represents the context for the current operation. This object
  is used to track requests to the storage service, and to provide additional runtime information about
  the operation.
  
  @return A {@link FileOutputStream} object used to write data to the file.
  
  @throws StorageException
  If a storage service error occurred.
  @throws URISyntaxException