Potential bug in the nullability data flow?

Version Used: I’m on the latest net5.0 RC1 SDK

Steps to Reproduce: As I was adding nullable annotations to System.Net.HttpListener, I ran into this. I have this method:

internal static void FillFromString(NameValueCollection nvc, string s, bool urlencoded, Encoding encoding)
            {
                int l = (s != null) ? s.Length : 0;
                int i = (s.Length > 0 && s[0] == '?') ? 1 : 0;

I see an error at s.Length saying "Dereference of possible null reference. But sis defined as astring(notstring?) so it can never be null. I suspect the s != nullline is changing the nullability information. If I changes != nulltos != “foo”`, the error goes away.

Expected Behavior: No error at s.Length. Potentially report that the ternary operator at (s != null) can be removed (this is not strictly required to fix this bug)

Actual Behavior: Error at s.Length.

[RikkiGibson]

Will close this out now, feel free to follow up here if you have questions.

[pgovind]

Apologies, I was busy with .NET 5 stuff. If this is by design, I agree that this can be closed!