code: def add_annotation_type(self, doc, annotation_type):
          
          if len(doc.annotations) != 0:
              if not self.annotation_type_set:
                  self.annotation_type_set = True
                  if validations.validate_annotation_type(annotation_type):
                      doc.annotations[-1].annotation_type = annotation_type
                      return True
                  else:
                      raise SPDXValueError('Annotation::AnnotationType')
              else:
                  raise CardinalityError('Annotation::AnnotationType')
          else:
              raise OrderError('Annotation::AnnotationType')
docs: Sets the annotation type. Raises CardinalityError if
          already set. OrderError if no annotator defined before.
          Raises SPDXValueError if invalid value.