Structures without members are not encoded properly

[Supertuba12]

Structures without members are not encoded properly

The JSON RPC API specification for 'eth_signTypedData_v4' does not
explicitly state that the required struct 'EIP712Domain' has to define
any members [1]. The current implementation cannot correctly encode
such a structure, as it assumes that at least one member has been
parsed and added to the struct's string representation.

[1] https://eips.ethereum.org/EIPS/eip-712#specification-of-the-eth_signtypeddata-json-rpc

Steps To Reproduce

Pass a valid structured data object where a type structure lacks a member:

{
  "types": {
    "EIP712Domain": []
  },
  "primaryType": "EIP712Domain",
  "domain": {},
  "message": {}
}

Expected behavior

The internal function encodeStruct should return "EIP712Domain()" when encoding EIP712Domain.

Actual behavior

The internal function returns "EIP712Domain)"

Environment

• Web3j version: First found using the latest android release 4.8.8-android. Reproduced on master ac0618c4d38ca780a7781d58255ff8b38626d7fc

[NickSneo]

Thanks for reporting and contributing.

[NickSneo]

PR merged