Needed a one liner guard function for C# that doesn't thrown an exception.

Guard.cs

/*
Example Usage:
public int CalcScore(VideoResolution? itemResolution) {
    if (Util.Guard(out VideoResolution res, itemResolution)) return 0;
    if (res == VideoResolution._1080p) return 5;
    return 1;
}

Alternatively you can do:
if (!(itemResolution is VideoResolution res)) return 0;

in C#9:
if (itemResolution is not VideoResolution res) return 0;
*/
public static class Util {
    public static bool Guard<T>(out T target, T? source) where T: class {
        if (source == null) { 
            target = null;
            return true;
        }
        target = source;
        return false;
    }

    public static bool Guard<T>(out T target, T? source) where T: struct {
        if (source == null) { 
            target = default(T);
            return true;
        }
        target = (T)source;
        return false;
    }
}