message: Decode null as BN without failing
diff: import { Param$Decoded } from '../../types';
  +import BN from 'bn.js';
  import u8aToBn from '@polkadot/util/u8a/toBn';
  export default function bn (input: Uint8Array, bitLength: 32 | 64 | 128): Param$Decoded {
  @@ -11,6 +12,8 @@ export default function bn (input: Uint8Array, bitLength: 32 | 64 | 128): Param$
  return {
  length,
  - value: u8aToBn(input.subarray(0, length), true)
  + value: input
  + ? u8aToBn(input.subarray(0, length), true)
  + : new BN(0)
  };
  }
  