code: def add_annotation_date(self, doc, annotation_date):
          
          if len(doc.annotations) != 0:
              if not self.annotation_date_set:
                  self.annotation_date_set = True
                  date = utils.datetime_from_iso_format(annotation_date)
                  if date is not None:
                      doc.annotations[-1].annotation_date = date
                      return True
                  else:
                      raise SPDXValueError('Annotation::AnnotationDate')
              else:
                  raise CardinalityError('Annotation::AnnotationDate')
          else:
              raise OrderError('Annotation::AnnotationDate')
docs: Sets the annotation date. Raises CardinalityError if
          already set. OrderError if no annotator defined before.
          Raises SPDXValueError if invalid value.