NullType Sentinels

nulltype is a Python library (current version 2.3.1) that provides custom null values and sentinels, distinct from Python's built-in `None`, `False`, or `True`. It helps represent different states of 'emptiness' or 'undefined' values, such as `Passthrough`, `Prohibited`, or `Undefined`, without overloading standard Python nullish objects. The library aims to simplify code by allowing robust handling of potentially missing data in a consistent way. The last release was in June 2018, indicating a maintenance phase with infrequent updates.