[Bug] Right-click context menu fails to appear on most custom nodes

### Prerequisites

- [x] I am running the latest version of ComfyUI
- [x] I have searched existing issues to make sure this isn't a duplicate
- [x] I have tested with all custom nodes disabled ([see how](https://docs.comfy.org/troubleshooting/custom-node-issues#step-1%3A-test-with-all-custom-nodes-disabled))

### What happened?

### Description

After a recent update, the right-click context menu has stopped working for the majority of custom nodes. When I right-click on most custom nodes, no menu appears.

Notably, the right-click functionality on the blank canvas (for adding nodes) works correctly as expected.

**Error Message:**
`Uncaught TypeError: Cannot read properties of null (reading 'content') at index.js:543`

**Analysis from the Call Stack:**
The error originates from `LGraphCanvas.getNodeMenuOptions` which then calls `nodetype.getExtraMenuOptions`. This suggests that a recent change in the core ComfyUI frontend has created a breaking change for how many custom nodes add their extra menu options. The issue appears to be a core incompatibility rather than a bug in a single custom node, as multiple nodes are present in the call stack leading to the error.

### Environment Details

* **OS:** Windows 11
* **ComfyUI Version:** 0.3.52
* **comfyui_frontend_package:** 1.26.6
* **Browser:** Google Chrome 139.0.7258.139

### Steps to Reproduce

### Steps to Reproduce

1. Load any workflow with various custom nodes.
2. Right-click on a custom node.

### Behavior

* **Expected behavior:** A context menu with options (e.g., Bypass, Colors, etc.) should appear.
* **Actual behavior:** Nothing happens. The context menu does not show up for most custom nodes.

Please see the attached screenshot for the full console output. This should provide a clear path for debugging.

### How is this affecting you?

Feature doesn't work as expected

### ComfyUI Frontend Version

1.26.6

### Browser

Chrome/Chromium

### Console Errors

```javascript

```

### Logs

```shell
[ERROR] An error occurred while retrieving information for the 'PromptComposerEffect' node.
Traceback (most recent call last):
File "B:\comfyui\server.py", line 634, in get_object_info
out[x] = node_info(x)
^^^^^^^^^^^^
File "B:\comfyui\server.py", line 595, in node_info
if issubclass(obj_class, _ComfyNodeInternal):
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
TypeError: issubclass() arg 1 must be a class
```

### Additional Context

_No response_

┆Issue is synchronized with this [Notion page](https://www.notion.so/Issue-5186-Bug-Right-click-context-menu-fails-to-appear-on-most-custom-nodes-2596d73d365081d3bf2afe2b59043263) by [Unito](https://www.unito.io)