code: def add_reviewer(self, doc, reviewer):
          
          # Each reviewer marks the start of a new review object.
          # FIXME: this state does not make sense
          self.reset_reviews()
          if validations.validate_reviewer(reviewer):
              doc.add_review(review.Review(reviewer=reviewer))
              return True
          else:
              raise SPDXValueError('Review::Reviewer')
docs: Adds a reviewer to the SPDX Document.
          Reviwer is an entity created by an EntityBuilder.
          Raises SPDXValueError if not a valid reviewer type.