C# has || just like any other language, but objects aren't truthy and nulls aren't falsy. This was a good design decision, since it catches the common = vs. == error if(a=b) while doing the type check rather than silently doing the (probably) wrong thing. As a consequence, the || doesn't work as it does in other places. Hence ??.

Every language?

Java, as far as I know, does not allow if (someObject) where someObject is a class type. AFIAK, java only allows that if someObject is a bool, or possibly an int as well.

In strongly typed languages in general, null is not the same thing as false and not-null is not the same thing as true.