class_docstr: An mapping operation was requested for an unknown class.
class_docstr_tok: ["An","mapping","operation","was","requested","for","an","unknown","class","."]
code: def __init__(self, cls: Type[_T], msg: Optional[str] = None):
      if not msg:
          msg = _default_unmapped(cls)
      UnmappedError.__init__(self, msg)
  
imports: from __future__ import annotations
  from typing import Any
  from typing import Optional
  from typing import Tuple
  from typing import Type
  from typing import TYPE_CHECKING
  from typing import TypeVar
  from ..None import exc
  from ..None import util
  from ..exc import MultipleResultsFound
  from ..exc import NoResultFound
label_desc: Use image node_id 1 to create a new UnmappedClassError object from inherited base classes: UnmappedError with example: obj = UnmappedClassError(cls, msg)