GraphQLUpload with processRequest on apollo-server-micro not working
When uploading a file im getting the following error.

![imagen](https://user-images.githubusercontent.com/19596334/143669581-fc0db7c4-2d74-44d6-af33-49e61471c5b8.png)

Server code:
```
const apolloServer = new ApolloServer({
  credentials: true,
  typeDefs: mergeTypeDefs(loadFilesSync(path.join(process.cwd(), 'graphql/schemas'))),
  resolvers: mergeResolvers([...Mutation, ...Query, ...types]),
  context: async ({ req, res }) => {
    const username = req.session.get('username')
    return { db, req, res, username, user: username && await db.models.user.findByPk(username) }
  }
})
const startServer = apolloServer.start()

export default withSession(async (req, res) => {
  res.setHeader('Access-Control-Allow-Origin', '*')
  res.setHeader('Access-Control-Allow-Credentials', 'true')
  res.setHeader('Access-Control-Allow-Headers', 'Origin, X-Requested-With, Content-Type, Accept')

  const contentType = req.headers['content-type']
  if (contentType && contentType.startsWith('multipart/form-data')) {
    req.filePayload = await processRequest(req, res)
  }

  await db.sync()
  await startServer

  return apolloServer.createHandler({ path: '/api/graphql' })(req, res)
})

export const config = {
  api: { bodyParser: false }
}
```

Resolvers object:
![imagen](https://user-images.githubusercontent.com/19596334/143669609-2aff36d5-e4fc-4892-8f3a-68ee12843f99.png)
