Adjust for zero-length combines (#2369)

packages/api-derive/package.json

@@ -32,13 +32,13 @@
     "@polkadot/rpc-core": "1.20.0-beta.4",
     "@polkadot/rpc-provider": "1.20.0-beta.4",
     "@polkadot/types": "1.20.0-beta.4",
-    "@polkadot/util": "^2.14.1",
-    "@polkadot/util-crypto": "^2.14.1",
+    "@polkadot/util": "^2.15.0-beta.0",
+    "@polkadot/util-crypto": "^2.15.0-beta.0",
     "bn.js": "^5.1.2",
     "memoizee": "^0.4.14",
     "rxjs": "^6.5.5"
   },
   "devDependencies": {
-    "@polkadot/keyring": "^2.14.1"
+    "@polkadot/keyring": "^2.15.0-beta.0"
   }
 }

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(