Add swapRegistry(hash?) to initlize clean registry (#2534)

* Add swapRegistry(hash?) to initlize clean registry

* Cater for genesisHash queries

packages/api-derive/src/imOnline/receivedHeartbeats.ts

@@ -9,6 +9,7 @@ import { Observable, of, combineLatest } from 'rxjs';
 import { map, switchMap } from 'rxjs/operators';
 import { ApiInterfaceRx } from '@polkadot/api/types';
 import { Bytes, Option, u32 } from '@polkadot/types';
+import { BN_ZERO } from '@polkadot/util';
 
 import { memo } from '../util';
 
@@ -34,7 +35,7 @@ export function receivedHeartbeats (api: ApiInterfaceRx): () => Observable<Deriv
             [validator.toString()]: {
               blockCount: numBlocks[index],
               hasMessage: !heartbeats[index].isEmpty,
-              isOnline: !heartbeats[index].isEmpty || numBlocks[index].gtn(0)
+              isOnline: !heartbeats[index].isEmpty || numBlocks[index].gt(BN_ZERO)
             }
           }), {})
         )

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

@@ -8,6 +8,7 @@ import { DeriveEraPoints, DeriveEraValPoints } from '../types';
 
 import { Observable, of } from 'rxjs';
 import { map, switchMap } from 'rxjs/operators';
+import { BN_ZERO } from '@polkadot/util';
 
 import { deriveCache, memo } from '../util';
 
@@ -15,7 +16,7 @@ const CACHE_KEY = 'eraPoints';
 
 function mapValidators ({ individual }: EraRewardPoints): DeriveEraValPoints {
   return [...individual.entries()]
-    .filter(([, points]): boolean => points.gtn(0))
+    .filter(([, points]) => points.gt(BN_ZERO))
     .reduce((result: DeriveEraValPoints, [validatorId, points]): DeriveEraValPoints => {
       result[validatorId.toString()] = points;