for mol in ligands: TypeError: 'NoneType' object is not iterable

[RJ-Li]

Please help me checking my script to predict on my ./coreset:

import os
import pandas as pd
import csv
import oddt
from oddt.scoring.functions import RFScore
oddt.toolkit = oddt.toolkits.rdk

# create RFScore model from trained model
# rf = RFScore.load('/path/to/your/model.pkl')

rf = RFScore.rfscore(version=1, n_jobs=-1)

with open('result_csv.csv', 'w', newline='') as csvfile:
    fieldnames = ['pdb_id', 'rf_score_v1']
    writer = csv.DictWriter(csvfile, fieldnames=fieldnames)
    writer.writeheader()

    for root, dirs, _ in os.walk('./coreset'):
        for dir in dirs:
            pdb_id = dir 
            ligands_file = os.path.join(root, dir, f'{pdb_id}_ligand.sdf')
            proteins_file = os.path.join(root, dir, f'{pdb_id}_pocket.pdb')
            lig_mol = next(oddt.toolkit.readfile('sdf', ligands_file))
            prot_mol = next(oddt.toolkit.readfile('pdb', proteins_file))
            score = rf.predict(lig_mol, prot_mol)
            print(f'{pdb_id}_ligand.sdf', score)

Traceback (most recent call last):
File "oddt_rfscore_Coreset.py", line 25, in
score = rf.predict(lig_mol, prot_mol)
File "/data2/rjli/mambaforge/envs/oddt/lib/python3.8/site-packages/oddt/scoring/init.py", line 260, in predict
descs = self.descriptor_generator.build(ligands)
File "/data2/rjli/mambaforge/envs/oddt/lib/python3.8/site-packages/oddt/scoring/descriptors/init.py", line 167, in build
for mol in ligands:
TypeError: 'NoneType' object is not iterable