Cannot decode height 1 - Error in parsing for rollapps

[Segfaultd]

Introduction

Using tendermint RPC, it is impossible to query the height 1 when the last_commit (genesis) signatures object is null. That's the case on a Rollapp implementation, which has no builtin validator set.
It fails to decode the block, because it expects here to be an array
https://github.com/cosmos/cosmjs/blob/main/packages/tendermint-rpc/src/comet38/adaptor/responses.ts#L491

Stack trace

Error: Value must not be null
    at assertSet (/Users/segfaultd/dev/orbit-codes/bridge/node_modules/@cosmjs/tendermint-rpc/src/comet38/encodings.ts:17:11)
    at assertArray (/Users/segfaultd/dev/orbit-codes/bridge/node_modules/@cosmjs/tendermint-rpc/src/comet38/encodings.ts:72:3)
    at decodeCommit (/Users/segfaultd/dev/orbit-codes/bridge/node_modules/@cosmjs/tendermint-rpc/src/comet38/adaptor/responses.ts:491:28)
    at decodeBlock (/Users/segfaultd/dev/orbit-codes/bridge/node_modules/@cosmjs/tendermint-rpc/src/comet38/adaptor/responses.ts:795:50)
    at decodeBlockResponse (/Users/segfaultd/dev/orbit-codes/bridge/node_modules/@cosmjs/tendermint-rpc/src/comet38/adaptor/responses.ts:811:12)
    at decodeBlock (/Users/segfaultd/dev/orbit-codes/bridge/node_modules/@cosmjs/tendermint-rpc/src/comet38/adaptor/responses.ts:849:12)
    at Comet38Client.doCall (/Users/segfaultd/dev/orbit-codes/bridge/node_modules/@cosmjs/tendermint-rpc/src/comet38/comet38client.ts:347:12)
    at processTicksAndRejections (node:internal/process/task_queues:95:5)
    at BlockService.sync (/Users/segfaultd/dev/orbit-codes/bridge/src/features/block/services/block.service.ts:129:25)
    at BlocksController.getByHeight (/Users/segfaultd/dev/orbit-codes/bridge/src/features/block/http/controllers/blocks.controller.ts:39:23)

Block structure

{
   "block_id":{
      "hash":"617E8F71CC8D555B0D30D2628C919C0DB20F9AFA07E3AA547DF3CBB999B9B33C",
      "parts":{
         "total":1,
         "hash":"617E8F71CC8D555B0D30D2628C919C0DB20F9AFA07E3AA547DF3CBB999B9B33C"
      }
   },
   "block":{
      "header":{
         "version":{
            "block":"11"
         },
         "chain_id":"test-network-1",
         "height":"1",
         "time":"2024-04-30T05:41:58.005961781Z",
         "last_block_id":{
            "hash":"0000000000000000000000000000000000000000000000000000000000000000",
            "parts":{
               "total":1,
               "hash":"0000000000000000000000000000000000000000000000000000000000000000"
            }
         },
         "last_commit_hash":"E3B0C44298FC1C149AFBF4C8996FB92427AE41E4649B934CA495991B7852B855",
         "data_hash":"E3B0C44298FC1C149AFBF4C8996FB92427AE41E4649B934CA495991B7852B855",
         "validators_hash":"6B52BC5E14DCEC36FCB8A2709B7D4967D58BBB78D1BA42A373784E3F172B2728",
         "next_validators_hash":"6B52BC5E14DCEC36FCB8A2709B7D4967D58BBB78D1BA42A373784E3F172B2728",
         "consensus_hash":"0000000000000000000000000000000000000000000000000000000000000000",
         "app_hash":"E3B0C44298FC1C149AFBF4C8996FB92427AE41E4649B934CA495991B7852B855",
         "last_results_hash":"E3B0C44298FC1C149AFBF4C8996FB92427AE41E4649B934CA495991B7852B855",
         "evidence_hash":"E3B0C44298FC1C149AFBF4C8996FB92427AE41E4649B934CA495991B7852B855",
         "proposer_address":"6F4C4E4482AC111E9EA4D4450869889AF738046A"
      },
      "data":{
         "txs":null
      },
      "evidence":{
         "evidence":null
      },
      "last_commit":{
         "height":"0",
         "round":0,
         "block_id":{
            "hash":"617E8F71CC8D555B0D30D2628C919C0DB20F9AFA07E3AA547DF3CBB999B9B33C",
            "parts":{
               "total":1,
               "hash":"617E8F71CC8D555B0D30D2628C919C0DB20F9AFA07E3AA547DF3CBB999B9B33C"
            }
         },
         "signatures":null
      }
   }
}

Proposed fix

Can we make that check optional, or at least give it a default empty array in case of empty signatures prop ?

Used versions

"dependencies": {
    "@cosmjs/amino": "^0.32.2",
    "@cosmjs/crypto": "^0.32.2",
    "@cosmjs/encoding": "^0.32.2",
    "@cosmjs/json-rpc": "^0.32.2",
    "@cosmjs/proto-signing": "^0.32.2",
    "@cosmjs/stargate": "^0.32.2",
    "@cosmjs/tendermint-rpc": "^0.32.2",
    "@cosmjs/utils": "^0.32.2",
    "@cosmology/lcd": "^0.13.3"
  }