docs: def of(cls, *passages: BioCPassage):
          """
          Returns a collection passages
          """
          if len(passages) <= 0:
              raise ValueError("There has to be at least one passage.")
          c = BioCDocument()
          for passage in passages:
              if passage is None:
                  raise ValueError('Passage is None')
              c.add_passage(passage)
          return c