Fix an issue introduced in 0.3.0 where unvalid child leads to wrong naming in the DataFrame outputted by DarkSol.query() method. - Raise an error again if a membership is not found.
Fix an issue introduced in 0.3.0 where unvalid child leads to wrong naming in the DataFrame outputted by DarkSol.query() method. - Raise an error again if a membership is not found.