Find the bug in this FastAPI file saving code:

Find the bug in this FastAPI file saving code:

from fastapi import FastAPI, File, UploadFile
app = FastAPI()

@app.post('/upload')
async def upload(file: UploadFile = File(...)):
    with open(file.filename, 'wb') as f:
        content = await file.read()
        f.write(content)
    return {'filename': file.filename}