Return the values for this attribute as stored in an AFF4Object.

def GetValues(self, fd):
    """Return the values for this attribute as stored in an AFF4Object."""
    result = None
    for result in fd.new_attributes.get(self, []):
      # We need to interpolate sub fields in this rdfvalue.
      if self.field_names:
        for x in self.GetSubFields(result, self.field_names):
          yield x

      else:
        yield result

    for result in fd.synced_attributes.get(self, []):
      result = result.ToRDFValue()

      # We need to interpolate sub fields in this rdfvalue.
      if result is not None:
        if self.field_names:
          for x in self.GetSubFields(result, self.field_names):
            yield x

        else:
          yield result

    if result is None:
      default = self.GetDefault(fd)
      if default is not None:
        yield default