Redirect inserting unexpected slash between index and parameters

[Ryan-Pierce]

The URL

https://example.com/Ryan

is redirecting to

https://example.com/index.html/?u=Ryan
                              ^
      unexpected trailing slash

My configurations are as follows:

...
  {
    "redirects": [
      {
        "regex": "/(\\w+)",
        "destination": "/index.html?u=:1",
        "type": 301
      }
    ],
    "trailingSlash": false
  }

I don't expect that slash in the redirected URL since it is not in my destination. Is my understanding wrong? How can I remove the unexpected slash?