code: def valid(self):
          
          if self.end is None:
              if self.start is not None:
                  return self.start <= datetime.datetime.utcnow()
              else:
                  return True
          else:
              if self.start is not None:
                  return self.start <= datetime.datetime.utcnow() <= self.end
              else:
                  return datetime.datetime.utcnow() <= self.end
docs: Checks if the lease is currently valid (not expired and not in the future)
          :return: bool: True if lease is valid