[Bug] [MultiGPU/DDP] TypeError: expected str, bytes or os.PathLike object, not NoneType

1. Did you update? `pip install --upgrade unsloth unsloth_zoo`  **yes**
2. `Colab` or `Kaggle` or local / cloud  **local**
3. Number GPUs used, use `nvidia-smi`  **2**
4. Which notebook? Please link!  [https://docs.unsloth.ai/basics/multi-gpu-training-with-unsloth/ddp](url)
5. Which Unsloth version, TRL version, transformers version, PyTorch version?  **PyTorch**
6. Which trainer? `SFTTrainer`, `GRPOTrainer` etc  **used Unsloth cli**

I ran the following (using the instructions on the linked DDP fine-tuning tutorial) and encountered the resulting error (see the bash log below):

```bash
torchrun --nproc_per_node=2 unsloth-cli.py   --model_name=Qwen/Qwen3-8B   --dataset=yahma/alpaca-cleaned --save_model

W1211 01:23:30.336000 22744 torch/distributed/run.py:803] 
W1211 01:23:30.336000 22744 torch/distributed/run.py:803] *****************************************
W1211 01:23:30.336000 22744 torch/distributed/run.py:803] Setting OMP_NUM_THREADS environment variable for each process to be 1 in default, to avoid your system being overloaded, please further tune the variable for optimal performance in your application as needed. 
W1211 01:23:30.336000 22744 torch/distributed/run.py:803] *****************************************
🦥 Unsloth: Will patch your computer to enable 2x faster free finetuning.
🦥 Unsloth: Will patch your computer to enable 2x faster free finetuning.
🦥 Unsloth Zoo will now patch everything to make training faster!
🦥 Unsloth Zoo will now patch everything to make training faster!
Traceback (most recent call last):
  File "/home/my-user/development/unsloth2/unsloth/unsloth/lib/python3.12/site-packages/unsloth_zoo/compiler.py", line 672, in create_new_function
    new_module, old_path = import_module(compile_folder, name)
                           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/home/my-user/development/unsloth2/unsloth/unsloth/lib/python3.12/site-packages/unsloth_zoo/compiler.py", line 668, in import_module
    raise e
  File "/home/my-user/development/unsloth2/unsloth/unsloth/lib/python3.12/site-packages/unsloth_zoo/compiler.py", line 663, in import_module
    new_module = importlib.import_module(name)
                 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/usr/lib/python3.12/importlib/__init__.py", line 90, in import_module
    return _bootstrap._gcd_import(name[level:], package, level)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "<frozen importlib._bootstrap>", line 1387, in _gcd_import
  File "<frozen importlib._bootstrap>", line 1360, in _find_and_load
  File "<frozen importlib._bootstrap>", line 1324, in _find_and_load_unlocked
ModuleNotFoundError: No module named 'UnslothBCOTrainer'

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File "/home/my-user/development/unsloth2/unsloth/unsloth-cli.py", line 441, in <module>
    run(args)
  File "/home/my-user/development/unsloth2/unsloth/unsloth-cli.py", line 37, in run
    from unsloth import FastLanguageModel
  File "/home/my-user/development/unsloth2/unsloth/unsloth/__init__.py", line 257, in <module>
    from .models import *
  File "/home/my-user/development/unsloth2/unsloth/unsloth/models/__init__.py", line 15, in <module>
    from .llama import FastLlamaModel
  File "/home/my-user/development/unsloth2/unsloth/unsloth/models/llama.py", line 3400, in <module>
    PatchFastRL(FastLanguageModel = FastLlamaModel)
  File "/home/my-user/development/unsloth2/unsloth/unsloth/models/rl.py", line 1347, in PatchFastRL
    patch_trl_rl_trainers()
  File "/home/my-user/development/unsloth2/unsloth/unsloth/models/rl.py", line 1333, in patch_trl_rl_trainers
    _patch_trl_rl_trainers(trainer)
  File "/home/my-user/development/unsloth2/unsloth/unsloth/models/rl.py", line 1003, in _patch_trl_rl_trainers
    created_module = create_new_function(
                     ^^^^^^^^^^^^^^^^^^^^
  File "/home/my-user/development/unsloth2/unsloth/unsloth/lib/python3.12/site-packages/unsloth_zoo/compiler.py", line 678, in create_new_function
    function_location = os.path.join(compile_folder, f"{name}.py")
                        ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "<frozen posixpath>", line 76, in join
TypeError: expected str, bytes or os.PathLike object, not NoneType
/home/my-user/development/unsloth2/unsloth/unsloth/models/rl_replacements.py:946: UserWarning: You are importing from 'trl.experimental'. APIs here are unstable and may change or be removed without notice. Silence this warning by setting environment variable TRL_EXPERIMENTAL_SILENCE=1.
  import trl.experimental.openenv.utils as openenv_utils
[unsloth_zoo.log|WARNING]Unsloth: Failed to import trl openenv: No module named 'trl.experimental.openenv'
W1211 01:23:34.640000 22744 torch/distributed/elastic/multiprocessing/api.py:908] Sending process 22782 closing signal SIGTERM
E1211 01:23:34.755000 22744 torch/distributed/elastic/multiprocessing/api.py:882] failed (exitcode: 1) local_rank: 1 (pid: 22783) of binary: /home/my-user/development/unsloth2/unsloth/unsloth/bin/python
Traceback (most recent call last):
  File "/home/my-user/development/unsloth2/unsloth/unsloth/bin/torchrun", line 7, in <module>
    sys.exit(main())
             ^^^^^^
  File "/home/my-user/development/unsloth2/unsloth/unsloth/lib/python3.12/site-packages/torch/distributed/elastic/multiprocessing/errors/__init__.py", line 357, in wrapper
    return f(*args, **kwargs)
           ^^^^^^^^^^^^^^^^^^
  File "/home/my-user/development/unsloth2/unsloth/unsloth/lib/python3.12/site-packages/torch/distributed/run.py", line 936, in main
    run(args)
  File "/home/my-user/development/unsloth2/unsloth/unsloth/lib/python3.12/site-packages/torch/distributed/run.py", line 927, in run
    elastic_launch(
  File "/home/my-user/development/unsloth2/unsloth/unsloth/lib/python3.12/site-packages/torch/distributed/launcher/api.py", line 156, in __call__
    return launch_agent(self._config, self._entrypoint, list(args))
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/home/my-user/development/unsloth2/unsloth/unsloth/lib/python3.12/site-packages/torch/distributed/launcher/api.py", line 293, in launch_agent
    raise ChildFailedError(
torch.distributed.elastic.multiprocessing.errors.ChildFailedError: 
============================================================
unsloth-cli.py FAILED
------------------------------------------------------------
Failures:
  <NO_OTHER_FAILURES>
------------------------------------------------------------
Root Cause (first observed failure):
[0]:
  time      : 2025-12-11_01:23:34
  host      : my-pc
  rank      : 1 (local_rank: 1)
  exitcode  : 1 (pid: 22783)
  error_file: <N/A>
  traceback : To enable traceback see: https://pytorch.org/docs/stable/elastic/errors.html
============================================================
```

Please advise how to rectify this.  For additional info, here's my nvidia-smi output:

```bash
+-----------------------------------------------------------------------------------------+
| NVIDIA-SMI 575.51.03              Driver Version: 575.51.03      CUDA Version: 12.9     |
|-----------------------------------------+------------------------+----------------------+
| GPU  Name                 Persistence-M | Bus-Id          Disp.A | Volatile Uncorr. ECC |
| Fan  Temp   Perf          Pwr:Usage/Cap |           Memory-Usage | GPU-Util  Compute M. |
|                                         |                        |               MIG M. |
|=========================================+========================+======================|
|   0  NVIDIA GeForce RTX 3090        Off |   00000000:01:00.0 Off |                  N/A |
| 40%   28C    P8             22W /  350W |      18MiB /  24576MiB |      0%      Default |
|                                         |                        |                  N/A |
+-----------------------------------------+------------------------+----------------------+
|   1  NVIDIA GeForce RTX 3090        Off |   00000000:02:00.0 Off |                  N/A |
| 40%   26C    P8              7W /  350W |      18MiB /  24576MiB |      0%      Default |
|                                         |                        |                  N/A |
+-----------------------------------------+------------------------+----------------------+
                                                                                         
+-----------------------------------------------------------------------------------------+
| Processes:                                                                              |
|  GPU   GI   CI              PID   Type   Process name                        GPU Memory |
|        ID   ID                                                               Usage      |
|=========================================================================================|
|    0   N/A  N/A            6167      G   /usr/lib/xorg/Xorg                        4MiB |
|    1   N/A  N/A            6167      G   /usr/lib/xorg/Xorg                        4MiB |
+-----------------------------------------------------------------------------------------+
```


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[Bug] [MultiGPU/DDP] TypeError: expected str, bytes or os.PathLike object, not NoneType #3722

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[Bug] [MultiGPU/DDP] TypeError: expected str, bytes or os.PathLike object, not NoneType #3722

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