Please use FileSystem tools to finish the following task:

### Task Description

There is a bug in the VoteNet backbone module that needs to be identified and fixed.

### Task Objectives

1. **Examine the codebase** using filesystem MCP tools
2. **Identify the bug** inside the hole process
3. **Fix the bug** in the code
4. **Create an answer file** with the bug location

### Expected Output

1. **Fix the bug** in the code file directly
2. **Create `answer.txt`** in the test directory root with the format: `path`

**Requirements:**

- Only include the bug's file path in answer.txt
- No additional text or explanation

### Hint

**The bug is not in demo.py**, please look deeper inside the codebase.
