class_docstr: Specifies how values should be parsed when creating a :class:`.Table`.
  
  :param null_values: A sequence of values which should be cast to
      :code:`None` when encountered by this data type.
class_docstr_tok: ["Specifies","how","values","should","be","parsed","when","creating","a",":","class",":","`",".Table","`",".",":","param","null_values",":","A","sequence","of","values","which","should","be","cast","to",":","code",":","`","None","`","when","encountered","by","this","data","type","."]
code: def __init__(self, null_values=DEFAULT_NULL_VALUES):
      self.null_values = [v.lower() for v in null_values]
  
imports: from agate.exceptions import CastError
label_desc: Use image node_id 1 to create a new DataType object  with example: obj = DataType(null_values)