File uploading works only with /parse in serverURL ('http://localhost:1337/parse')

New Issue Checklist

• I am not disclosing a vulnerability.
• I am not just asking a question.
• I have searched through existing issues.
• I can reproduce the issue with the latest version of Parse Server.

Issue Description

I can use a files uploading feature without errors (error: {"error":"Unexpected token - in JSON at position 0"}) only if I set '/parse' as a mount point in server's config:

mountPath: /parse
serverURL: http://localhost:1337/parse
publicServerURL: http://localhost:1337/parse

So Is it critical requirement to use '/parse' as a mount point? Or there is a way to escape such point and have URLs without /parse?

Steps to reproduce

Try to remove /parse

Actual Outcome

Expected Outcome

Environment

Server

• Parse Server version: 6.0.0
• Operating system: Linux Mint 20.2 Cinnamon and docker
• Local or remote host (AWS, Azure, Google Cloud, Heroku, Digital Ocean, etc): local

Database

• System (MongoDB or Postgres): MongoDB
• Database version: mongo:4
• Local or remote host (MongoDB Atlas, mLab, AWS, Azure, Google Cloud, etc): local

Client

• SDK (iOS, Android, JavaScript, PHP, Unity, etc): javascript
• SDK version: @types/parse": "^2.18.13

Logs

No source file or test is identified. Start by reproducing file uploads with mountPath, serverURL, and publicServerURL both using and omitting /parse, then trace the server's file-upload route and the reported JSON parsing error. Done means uploads work and produce correct URLs without requiring /parse, or the configuration requirement is documented clearly.