correctly initialize and expose empty sequences

src/sync/impl.ts

@@ -1065,7 +1065,7 @@ export abstract class BaseOrderedSequence<TElement> extends BaseSequence<TElemen
   }
 }
 
-export class EmptySequence<T> extends BaseSequence<T> {
+class EmptySequence<T> extends BaseSequence<T> {
   override nonEnumeratedCount() {
     return 0;
   }
@@ -1073,6 +1073,8 @@ export class EmptySequence<T> extends BaseSequence<T> {
   override *iterator() { }
 }
 
+export const EMPTY = new EmptySequence<any>();
+
 export class RangeSequence extends BaseSequence<number> {
   readonly #min: number;
   readonly #max: number;