docs: def from_conll(this_class, stream):
          """Construct a Sentence. stream is an iterable over strings where
          each string is a line in CoNLL-X format. If there are multiple
          sentences in this stream, we only return the first one."""
          stream = iter(stream)
          sentence = this_class()
          for line in stream:
              line = line.strip()
              if line:
                  sentence.append(Token.from_conll(line))
              elif sentence:
                  return sentence
          return sentence