Update OperationKinds.def

Author: alexfh

clang/include/clang/AST/OperationKinds.def

@@ -119,9 +119,9 @@ CAST_OPERATION(ArrayToPointerDecay)
 CAST_OPERATION(FunctionToPointerDecay)
 
 /// CK_NullToPointer - Null pointer constant to pointer, ObjC
-/// pointer, or block pointer.
+/// pointer, or block pointer. The result of this conversion can
+/// still be a null pointer constant if it has type std::nullptr_t.
 ///   (void*) 0
-///   (std::nullptr_t) x
 ///   void (^block)() = 0;
 CAST_OPERATION(NullToPointer)