  
  
  nlp_config_string = """
  [paths]
  train = ""
  dev = ""
  
  [corpora]
  
  [corpora.train]
  @readers = "spacy.Corpus.v1"
 
</s> remove train = ""
dev = ""
 </s> add train = null
dev = null </s> remove train = ""
dev = ""
 </s> add train = null
dev = null </s> remove     assert nlp2.config["corpora"]["train"]["path"] == ""
 </s> add     assert nlp2.config["corpora"]["train"]["path"] is None </s> remove     assert interpolated2["corpora"]["train"]["path"] == ""
 </s> add     assert interpolated2["corpora"]["train"]["path"] is None </s> remove     assert interpolated["corpora"]["train"]["path"] == ""
 </s> add     assert interpolated["corpora"]["train"]["path"] is None
train = null
dev = null
  
  
  nlp_config_string = """
  [paths]
train = null
dev = null
train = null
dev = null
  
  [corpora]
  
  [corpora.train]
  @readers = "spacy.Corpus.v1"
keep keep keep keep replace replace keep keep keep keep keep
 Make corpus paths default to None and improve errors 
spacy/tests/serialize/test_serialize_config.py