Use assertReturn to cleanup (#2804)

* Use assertReturn to cleanup

* Remove Uint/Int duplication

* Adjust

* ws errors, part 2

* .

* Adj. manual

* adj

* switchMap

* Revert "switchMap"

This reverts commit edfa4a2258f09042b61a27fd3812f0c53039fe4f.

* Revert.

* Revert.

* protected constructor

* Correct isHexJson flag

* Remove isHexJson (always detect)

* Adjust

* Flags

packages/api-contract/package.json

@@ -30,7 +30,7 @@
     "@polkadot/api": "^2.4.2-12",
     "@polkadot/rpc-core": "^2.4.2-12",
     "@polkadot/types": "^2.4.2-12",
-    "@polkadot/util": "^3.6.2-8",
+    "@polkadot/util": "^3.6.2-10",
     "bn.js": "^5.1.3",
     "rxjs": "^6.6.3"
   }