带有问题的代码

import { Injectable } from '@angular/core';
import { accountingTransactionsStoreService } from './accounting-transactions-store.service';
import { GeneralLedgeraccountsStoreService } from './general-ledger-accounts-store.service';
import { distinctUntilChanged,map,combineLatest } from 'rxjs/operators';

@Injectable({
  providedIn: 'root'
})
export class accountingReportsStoreService {


  constructor(
    private accountingTransactionsStore: accountingTransactionsStoreService,private   generalLedgeraccountsStore: GeneralLedgeraccountsStoreService) 
    {}

  readonly generalLedgeraccountsTransaction$
    = combineLatest(
      this.accountingTransactionsStore.selectedPeriodaccountingTransactionsflate$,this.generalLedgeraccountsStore.selectedOrganizationGeneralLedgeraccountsTree$)
      .pipe(distinctUntilChanged())
      .pipe(
        map(([transactionsflat,accountsTree]) => {
          if (transactionsflat && accountsTree)
            return [];
          else return [];
        })
      )
}

错误

  

类型'OperatorFunction '。