How to use the asynciterator.SingletonIterator function in asynciterator

context = context || ActionContext({});
    let subContext: ActionContext = context.delete(KEY_CONTEXT_SOURCE).delete(KEY_CONTEXT_SOURCES);
    const sourceType = this.forceSparqlEndpoint ? 'sparql' : 'auto';
    subContext = subContext.set(KEY_CONTEXT_SOURCES,
      AsyncReiterableArray.fromFixedData([{ type: sourceType, value: endpoint }]));

    // Query the source
    let output: IActorQueryOperationOutputBindings;
    try {
      output = ActorQueryOperation.getSafeBindings(
        await this.mediatorQueryOperation.mediate({ operation: pattern.input, context: subContext }));
    } catch (e) {
      if (pattern.silent) {
        // Emit a single empty binding
        output = {
          bindingsStream: new SingletonIterator(Bindings({})),
          type: 'bindings',
          variables: [],
        };
      } else {
        throw e;
      }
    }

    return output;
  }

public async runOperation(pattern: Algebra.Bgp, context: ActionContext)
  : Promise {
    return {
      bindingsStream: new SingletonIterator(Bindings({})),
      metadata: () => Promise.resolve({ totalItems: 1 }),
      type: 'bindings',
      variables: [],
    };
  }

undefined,
        enterConnection.id,
        exitConnection.id,
      );

      path.addStep(step);
      currentStopId = enterConnection.departureStop;
    }

    if (!path.steps.length) {
      return new EmptyIterator();
    }

    path.reverse();

    return new SingletonIterator(path);
  }