'Converts given RDFValue to other RDFValues.
Metadata object is provided by the caller. It contains basic information
about where the value is coming from (i.e. client_urn, session_id, etc)
as well as timestamps corresponding to when data was generated and
exported.
ExportConverter should use the metadata when constructing export-friendly
RDFValues.
Args:
metadata: ExportedMetadata to be used for conversion.
value: RDFValue to be converted.
token: Security token.
Yields:
Resulting RDFValues. Empty list is a valid result and means that
conversion wasn\'t possible. Resulting RDFValues may be of different
types.'

def Convert(self, metadata, value, token=None):

    raise NotImplementedError()
