Normally, in case of invalid input Uri() code throws UriFormatException. But with really weird input Uri(baseUri, Url) overload can produce NullReferenceException:

[TestMethod]
[ExpectedException(typeof(NullReferenceException))]
public void UriFailureTest()
{
    new Uri(
        new Uri("https://jobs.web.cern.ch/content/cern-jobs-insight/what-are-we-doing-while-you%E2%80%99re-waiting"),
        "https:/jobs.web.cern.ch/content/cern-jobs-insight/what-are-we-doing-while-you%E2%80%99re-waiting");
}