Setting useragent to null no longer works in 108.0.1

[drgrieve]

Describe the bug
Setting useragent to null now causes an exception = > The format of value ' ' is invalid

To Reproduce
Old code that worked (no useragent sent in headers)
var client = new RestClient("https://www.example.com.au");
client.UserAgent = null;

New code that fails
var client = new RestClient(new RestClientOptions { BaseUrl = new Uri("https://www.example.com.au"), UserAgent = null });

Stack trace
The format of value ' ' is invalid. Stack at System.Net.Http.Headers.HttpHeaderParser.ParseValue(String value, Object storeValue, Int32& index) at System.Net.Http.Headers.HttpHeaders.ParseAndAddValue(HeaderDescriptor descriptor, HeaderStoreItemInfo info, String value) at System.Net.Http.Headers.HttpHeaders.Add(HeaderDescriptor descriptor, String value) at System.Net.Http.Headers.HttpHeaderValueCollection`1.ParseAdd(String input) at RestSharp.RestClient.ConfigureHttpClient(HttpClient httpClient) at RestSharp.RestCl

[alexeyzimarev]

Maybe you can submit a PR where you check the property value for null and not assign anything.

[stale]

This issue has been automatically marked as stale because it has not had recent activity. It will be closed if no further activity occurs. Thank you for your contributions.

[repo-ranger]

⚠️ This issue has been marked wontfix and will be closed in 3 days

[stale]

This issue has been automatically marked as stale because it has not had recent activity. It will be closed if no further activity occurs. Thank you for your contributions.

[repo-ranger]

⚠️ This issue has been marked wontfix and will be closed in 3 days