Flow null state of default(T)

[mikernet]

The nullability state of the default(T) value should also flow like other variables so that code like this does not produce warnings:

var list = new List<object>();

if (default(T) != null) {
    list.Add(default(T)); // warning of possible null reference argument is unnecessary here
    T value = default; // value should be known to be not null here,
    list.Add(value); // so this should also work without a warning
}