class_docstr: Class to index 'Not Null' condition forsingle field in parquet dataset
class_docstr_tok: ["Class","to","index","'Not","Null","'","condition","forsingle","field","in","parquet","dataset"]
code: def __add__(self, other):
      if not isinstance(other, FieldNotNullIndexer):
          raise TypeError(
              "Make sure Spark map function return the same indexer type"
          )
      if self._column_name != other._column_name:
          raise ValueError(
              "Make sure indexers in Spark map function index the same fields"
          )
  
      self._index_data.update(other._index_data)
  
      return self
  
imports: import numpy
  from collections import defaultdict
  from petastorm.etl import RowGroupIndexerBase
label_desc: Use image node_id 2 for calling the FieldNotNullIndexer obj's underlying member method code with example usage: obj.__add__(other) and returns: self