Adjust for zero-length combines (#2369)

packages/api-derive/src/staking/electedInfo.ts

@@ -5,7 +5,7 @@
 import { ApiInterfaceRx } from '@polkadot/api/types';
 import { DeriveStakingElected } from '../types';
 
-import { Observable, combineLatest } from 'rxjs';
+import { Observable, combineLatest, of } from 'rxjs';
 import { map, switchMap } from 'rxjs/operators';
 
 import { memo } from '../util';
@@ -13,16 +13,20 @@ import { memo } from '../util';
 export function electedInfo (api: ApiInterfaceRx): () => Observable<DeriveStakingElected> {
   return memo((): Observable<DeriveStakingElected> =>
     api.derive.staking.validators().pipe(
-      switchMap(({ nextElected }): Observable<DeriveStakingElected> =>
-        combineLatest(
+      switchMap(({ nextElected }): Observable<DeriveStakingElected> => {
+        if (!nextElected.length) {
+          return of({ info: [], nextElected: [] });
+        }
+
+        return combineLatest(
           nextElected.map((accountId) => api.derive.staking.query(accountId))
         ).pipe(
           map((info): DeriveStakingElected => ({
             info,
             nextElected
           }))
-        )
-      )
+        );
+      })
     )
   );
 }

packages/api-derive/src/staking/waitingInfo.ts

@@ -5,7 +5,7 @@
 import { ApiInterfaceRx } from '@polkadot/api/types';
 import { DeriveStakingWaiting } from '../types';
 
-import { Observable, combineLatest } from 'rxjs';
+import { Observable, combineLatest, of } from 'rxjs';
 import { map, switchMap } from 'rxjs/operators';
 
 import { memo } from '../util';
@@ -20,6 +20,10 @@ export function waitingInfo (api: ApiInterfaceRx): () => Observable<DeriveStakin
         const elected = nextElected.map((a) => a.toString());
         const waiting = stashes.filter((v) => !elected.includes(v.toString()));
 
+        if (!waiting.length) {
+          return of({ info: [], waiting: [] });
+        }
+
         return combineLatest(
           waiting.map((accountId) => api.derive.staking.query(accountId))
         ).pipe(