VirtualFilePointerContainer (@NotNull Collection<String> urls) { // optimization: avoid creating heavy container for empty list, use 'EMPTY' stub for that case VirtualFilePointerContainer container; if (urls.isEmpty()) { container = EMPTY; } else { container = VirtualFilePointerManager.getInstance().createContainer(myRootsDisposable); ((VirtualFilePointerContainerImpl)container).addAll(urls); } return container; }