class_docstr: Dictionary with support for nans.
code: def __init__(self, mapping):
      super().__init__(mapping)
      for key, value in mapping.items():
          if is_scalar_nan(key):
              self.nan_value = value
              break
  
imports: from collections import Counter
  from contextlib import suppress
  from typing import NamedTuple
  import numpy
  from .None import is_scalar_nan
label_desc: Use image node_id 1 to create a new _nandict object from inherited base classes: dict with example: obj = _nandict(mapping)