Conditioning on the constraint column of the ColumnFormula constraint

[fealho]

Conditioning on the constraint column when using the ColumnFormula constraint causes the following error:

---------------------------------------------------------------------------
ValueError                                Traceback (most recent call last)
/var/folders/3p/f4b70gn5165464cqyvg157qw0000gn/T/ipykernel_42215/2787579389.py in <module>
----> 1 samples = model.sample(10, conditions={'b': 1})
      2 samples

~/Desktop/SDV/sdv/tabular/base.py in sample(self, num_rows, max_retries, max_rows_multiplier, conditions, float_rtol, graceful_reject_sampling)
    471             else:
    472                 transformed_conditions_in_group = transformed_conditions.loc[condition_indices]
--> 473                 transformed_groups = transformed_conditions_in_group.groupby(transformed_columns)
    474                 for transformed_group, transformed_dataframe in transformed_groups:
    475                     if not isinstance(transformed_group, tuple):

~/opt/anaconda3/envs/test/lib/python3.8/site-packages/pandas/core/frame.py in groupby(self, by, axis, level, as_index, sort, group_keys, squeeze, observed, dropna)
   6513         axis = self._get_axis_number(axis)
   6514 
-> 6515         return DataFrameGroupBy(
   6516             obj=self,
   6517             keys=by,

~/opt/anaconda3/envs/test/lib/python3.8/site-packages/pandas/core/groupby/groupby.py in __init__(self, obj, keys, axis, level, grouper, exclusions, selection, as_index, sort, group_keys, squeeze, observed, mutated, dropna)
    523             from pandas.core.groupby.grouper import get_grouper
    524 
--> 525             grouper, exclusions, obj = get_grouper(
    526                 obj,
    527                 keys,

~/opt/anaconda3/envs/test/lib/python3.8/site-packages/pandas/core/groupby/grouper.py in get_grouper(obj, key, axis, level, sort, observed, mutated, validate, dropna)
    819 
    820     if len(groupings) == 0 and len(obj):
--> 821         raise ValueError("No group keys passed!")
    822     elif len(groupings) == 0:
    823         groupings.append(Grouping(Index([], dtype="int"), np.array([], dtype=np.intp)))

ValueError: No group keys passed!

Code to reproduce it:

import pandas as pd
from sdv.constraints import *
from sdv.tabular import *

ones = [1 for i in range(10)]
data = pd.DataFrame({
    'a': ones,
    'b': ones,
    'c': ones
})

def formula(data):
    return data['a']

constraint = ColumnFormula(
    column='b',
    formula=formula
)

model = GaussianCopula(constraints=[constraint])
model.fit(data)
samples = model.sample(10, conditions={'b': 1})
samples