I try to send one strange request to bugzilla, and I need to add to query only key, without value.

Example:

```
bugzilla.com/rest/bug?resolution=FIXED&resolution=

```

I use typescript, and now, my code looks like:

```
let params = new HttpParams();
params = params.append('resolution', 'FIXED');
this.http.get('http://bugzilla.com/rest/bug', { params: params });

```

When I try to use:

```
append('resolution', '')

```

the result is wrong - I get: `resolution=""`

* `append('resolution', undefined)` turns into a wrong result, too: `resolution=undefined`
* `append('resolution', null)` also doesn't work and returns `resolution=null`

Can anybody help with this?