ussoewwin-ComfyUI-QwenImageLoraLoader/md/COMFYUI_PR_PROPOSAL.md

Fix: Multiple NoneType Errors in model_management.py Caused by Weakref-Based Model Lifecycle (10 Critical Locations)

Summary

This PR fixes multiple NoneType errors occurring across various nodes in ComfyUI 0.4.0 due to weakref-based model lifetime management.

The root cause is that LoadedModel.model may legitimately return None when the underlying ModelPatcher has been garbage collected—but several core functions do not guard against this scenario.

This results in unpredictable crashes such as:

• TypeError: 'NoneType' object is not callable
• AttributeError: 'NoneType' object has no attribute 'weights'
• AttributeError: 'NoneType' object has no attribute '__deepcopy__'

I identified 10 critical sites in model_management.py where lm.model must be checked for None before dereferencing.

Applying these checks eliminated every crash in my environment and also resolved multiple user-reported node failures (e.g., Issue #25).

Technical Root Cause

1. Weakref-based model ownership (0.4.0 change)

ComfyUI 0.4.0 introduced:

self._model = weakref.ref(model)

Meaning:

LoadedModel.model → returns None after GC

However, several core functions assume the model always exists.

2. Missing None checks in core memory/model routines

Affected functions include:

• is_dead()
• model_memory()
• model_loaded_memory()
• model_offloaded_memory()
• model_memory_required()
• model_unload()
• load_models_gpu() (3 locations)
• free_memory()

All of these iterate over LoadedModel objects and dereference lm.model without confirming it is non-None.

When GC collects a ModelPatcher during unloading, this leads to immediate crashes inside unrelated nodes.

3. Why this causes widespread node failures

When LoadedModel.model becomes None, the following operations fail across the system:

• memory estimation
• model pinning
• deepcopy
• device transition
• unload/load decisions

This produces dozens of different stack traces depending on timing, making it appear as though individual nodes are broken.

In reality, the issue comes from stale LoadedModel objects referencing collected ModelPatchers.

Fix

This PR adds explicit:

if lm.model is None:
    continue

or equivalent early returns in all affected locations.

After applying the patch:

• ✔ No remaining NoneType crashes
• ✔ Memory management behaves deterministically
• ✔ Model load/unload cycles no longer poison the cache state
• ✔ Third-party nodes stop failing as a side effect
• ✔ User-reported issue #25 (and similar) no longer reproduce

Why this patch is necessary

Weakref-based model ownership is correct by design.

However:

Any weakref dereference must treat None as a valid and expected state.

This invariant is currently violated in several core paths.

This PR ensures:

• Garbage-collected models no longer corrupt the model management pipeline
• All memory and lifecycle operations are robust against None
• LoadedModel remains safe even when backing objects are destroyed

I can provide:

• A complete diff
• Additional tests if needed
• Validation logs demonstrating stability after patching

Thank you for your work on ComfyUI—this patch should greatly stabilize the 0.4.0 model management system.