gethclient call fails if the `Code` property is not present in the state overrides

[simonovic86]

System information

go-ethereum version: v1.10.23
OS & Version: OSX

Expected behaviour

While using the gethclient/gethclient.go client to override the state with the gethclient/OverrideAccount properties, if the Code property is not present it should be omitted or set to null on marshal.

[
  {
    "data": "0xaa00000000000000000000000000000000000000",
    "from": "0xbb00000000000000000000000000000000000000",
    "to": "0xcc00000000000000000000000000000000000000"
  },
  "latest",
  {
    "0xdd00000000000000000000000000000000000000": {
      "nonce": "0x0",
      "code": null,
      "balance": null,
      "state": null,
      "stateDiff": null
    }
  }
]

Actual behaviour

If the Code property is not present in the overrides, it would still be marshalled into 0x because of the type hexutil.Bytes.

// Bytes marshals/unmarshals as a JSON string with 0x prefix.
// The empty slice marshals as "0x".
type Bytes []byte

The marshalled json:

[
  {
    "data": "0xaa00000000000000000000000000000000000000",
    "from": "0xbb00000000000000000000000000000000000000",
    "to": "0xcc00000000000000000000000000000000000000"
  },
  "latest",
  {
    "0xdd00000000000000000000000000000000000000": {
      "nonce": "0x0",
      "code": "0x",
      "balance": null,
      "state": null,
      "stateDiff": null
    }
  }
]

Because of this behaviour, the request fails with the execution reverted error.

Steps to reproduce the behaviour

// CallContract with override
override := gethclient.OverrideAccount{}

mapAcc := make(map[common.Address]gethclient.OverrideAccount)
mapAcc[address] = override

var err error
var result []byte

if result, err = client.CallContract(context.Background(), msg, nil, &mapAcc); err != nil {
	log.Fatalf("unexpected error: %v", err)
}

Backtrace

[backtrace]

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