code: def add_vt(self, vt_id, name=None, vt_params=None, vt_refs=None,
                 custom=None, vt_creation_time=None, vt_modification_time=None,
                 vt_dependencies=None, summary=None, impact=None, affected=None,
                 insight=None, solution=None, solution_t=None, detection=None,
                 qod_t=None, qod_v=None, severities=None):
          if not vt_id:
              return -2
          if self.vt_id_pattern.fullmatch(vt_id) is None:
              return -2
          if vt_id in self.vts:
              return -1
          if name is None:
              name = ''
          self.vts[vt_id] = {'name': name}
          if custom is not None:
              self.vts[vt_id]["custom"] = custom
          if vt_params is not None:
              self.vts[vt_id]["vt_params"] = vt_params
          if vt_refs is not None:
              self.vts[vt_id]["vt_refs"] = vt_refs
          if vt_dependencies is not None:
              self.vts[vt_id]["vt_dependencies"] = vt_dependencies
          if vt_creation_time is not None:
              self.vts[vt_id]["creation_time"] = vt_creation_time
          if vt_modification_time is not None:
              self.vts[vt_id]["modification_time"] = vt_modification_time
          if summary is not None:
              self.vts[vt_id]["summary"] = summary
          if impact is not None:
              self.vts[vt_id]["impact"] = impact
          if affected is not None:
              self.vts[vt_id]["affected"] = affected
          if insight is not None:
              self.vts[vt_id]["insight"] = insight
          if solution is not None:
              self.vts[vt_id]["solution"] = solution
              if solution_t is not None:
                  self.vts[vt_id]["solution_type"] = solution_t
          if detection is not None:
              self.vts[vt_id]["detection"] = detection
          if qod_t is not None:
              self.vts[vt_id]["qod_type"] = qod_t
          elif qod_v is not None:
              self.vts[vt_id]["qod"] = qod_v
          if severities is not None:
              self.vts[vt_id]["severities"] = severities
          return len(self.vts)