Missing structure hook for CompletionItem.documentation

[alcarney]

I get the following error while trying to structure a CompletionItem that provides a documentation field

>>> converter.structure(dict(label='example', documentation='This is documented'), CompletionItem)
  + Exception Group Traceback (most recent call last):
  |   File "<stdin>", line 1, in <module>
  |   File "/.../site-packages/cattrs/converters.py", line 309, in structure
  |     return self._structure_func.dispatch(cl)(obj, cl)
  |   File "<cattrs generated structure lsprotocol.types.CompletionItem>", line 117, in structure_CompletionItem
  |     if errors: raise __c_cve('While structuring ' + 'CompletionItem', errors, __cl)
  | cattrs.errors.ClassValidationError: While structuring CompletionItem (1 sub-exception)
  +-+---------------- 1 ----------------
    | Traceback (most recent call last):
    |   File "<cattrs generated structure lsprotocol.types.CompletionItem>", line 35, in structure_CompletionItem
    |     res['documentation'] = __c_structure_documentation(o['documentation'], __c_type_documentation)
    |   File "/.../site-packages/cattrs/converters.py", line 377, in _structure_error
    |     raise StructureHandlerNotFoundError(msg, type_=cl)
    | cattrs.errors.StructureHandlerNotFoundError: Unsupported type: typing.Union[str, lsprotocol.types.MarkupContent, NoneType]. Register a structure hook for it.
    | Structuring class CompletionItem @ attribute documentation
    +------------------------------------