Error in checkpoint merger

[dskmusic]

When I try to merge models, I get this error:

In webui:
Error loading/saving model file. It doesn't exist or the name contains illegal characters

In console:
Loading D:\SD-AUTOMATIC1111\stable-diffusion-webui\models\Stable-diffusion\dog_dskmulan.ckpt...
Loading D:\SD-AUTOMATIC1111\stable-diffusion-webui\models\Stable-diffusion\person_ksiluci.ckpt...
Merging...
100%|█████████████████████████████████████████████████████████████████████████████| 1131/1131 [00:08<00:00, 132.42it/s]
Error loading/saving model file:
Traceback (most recent call last):
File "D:\SD-AUTOMATIC1111\stable-diffusion-webui\modules\ui.py", line 1047, in modelmerger
results = run_modelmerger(*args)
File "D:\SD-AUTOMATIC1111\stable-diffusion-webui\modules\extras.py", line 196, in run_modelmerger
output_modelname = os.path.join(shared.cmd_opts.ckpt_dir, filename)
File "D:\Python\lib\ntpath.py", line 104, in join
path = os.fspath(path)
TypeError: expected str, bytes or os.PathLike object, not NoneType

some help¿
Thanks!