[BUG] .add_fold returns error

[blythed]

Code

db = superduper('mongomock://test_db')
q = db['docs'].select().add_fold('train')

Output

---------------------------------------------------------------------------
ValueError                                Traceback (most recent call last)
Cell In[6], line 1
----> 1 db['docs'].select().add_fold('train')

File ~/superduper-io/superduper/superduper/backends/base/query.py:35, in applies_to.<locals>.decorator.<locals>.decorated(self, *args, **kwargs)
     33     raise TypeError(msg)
     34 assert flavour in flavours, msg
---> 35 return f(self, *args, **kwargs)

File ~/.pyenv/versions/3.11.7/envs/superduper-3.11/lib/python3.11/site-packages/superduper_mongodb/query.py:370, in MongoQuery.add_fold(self, fold)
    364 @applies_to('find', 'find_one', 'select', 'outputs')
    365 def add_fold(self, fold: str):
    366     """Return a query that adds a fold to the query.
    367
    368     :param fold: The fold to add.
    369     """
--> 370     return self.filter(self['_fold'] == fold)

File ~/.pyenv/versions/3.11.7/envs/superduper-3.11/lib/python3.11/site-packages/superduper_mongodb/query.py:255, in MongoQuery.filter(self, *args, **kwargs)
    253     continue
    254 if not isinstance(arg, Query):
--> 255     raise ValueError(f'Filter arguments must be queries, but got: {arg}')
    256 assert len(arg.parts) > 1, f'Invalid filter query: {arg}'
    257 key, (op, op_args, _) = arg.parts[-2:]

ValueError: Filter arguments must be queries, but got: False

In [7]: db['docs'].select() == 2
Out[7]: False

In [8]: db['docs'].select().add_fold('train')
---------------------------------------------------------------------------
ValueError                                Traceback (most recent call last)
Cell In[8], line 1
----> 1 db['docs'].select().add_fold('train')

File ~/superduper-io/superduper/superduper/backends/base/query.py:35, in applies_to.<locals>.decorator.<locals>.decorated(self, *args, **kwargs)
     33     raise TypeError(msg)
     34 assert flavour in flavours, msg
---> 35 return f(self, *args, **kwargs)

File ~/.pyenv/versions/3.11.7/envs/superduper-3.11/lib/python3.11/site-packages/superduper_mongodb/query.py:370, in MongoQuery.add_fold(self, fold)
    364 @applies_to('find', 'find_one', 'select', 'outputs')
    365 def add_fold(self, fold: str):
    366     """Return a query that adds a fold to the query.
    367
    368     :param fold: The fold to add.
    369     """
--> 370     return self.filter(self['_fold'] == fold)

File ~/.pyenv/versions/3.11.7/envs/superduper-3.11/lib/python3.11/site-packages/superduper_mongodb/query.py:255, in MongoQuery.filter(self, *args, **kwargs)
    253     continue
    254 if not isinstance(arg, Query):
--> 255     raise ValueError(f'Filter arguments must be queries, but got: {arg}')
    256 assert len(arg.parts) > 1, f'Invalid filter query: {arg}'
    257 key, (op, op_args, _) = arg.parts[-2:]

ValueError: Filter arguments must be queries, but got: False