Redirect inserting unexpected slash between index and parameters

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?