Keep assetID hex as Option for toPayload

[TarikGul]

ref: #5967

This ensures that the HexString that is part of the SignerPayloadJSON is an Option.

[TarikGul]

So I tested this locally to send Assets over xcm with usdt as a asset to pay fees with and I am getting a wasm trap error:

2024-09-03 18:10:41        RPC-CORE: submitExtrinsic(extrinsic: Extrinsic): Hash:: 1002: Verification Error: Runtime error: Execution failed: Execution aborted due to trap: wasm trap: wasm `unreachable` instruction executed
WASM backtrace:
error while executing at wasm backtrace:
    0: 0x3f78ac - <unknown>!rust_begin_unwind
    1: 0x2113 - <unknown>!core::panicking::panic_fmt::hbb5a6b42001bdfec
    2: 0x34d3c8 - <unknown>!TaggedTransactionQueue_validate_transaction: RuntimeApi, Execution failed: Execution aborted due to trap: wasm trap: wasm `unreachable` instruction executed\nWASM backtrace:\nerror while executing at wasm backtrace:\n    0: 0x3f78ac - <unknown>!rust_begin_unwind\n    1: 0x2113 - <unknown>!core::pa…

[TarikGul]

The wasm trap issue above is fixed, but fees are not getting payed with usdt, but instead keeps defaulting to ksm... That being said I don't think that is a result of this PR!

[carlosala]

Very hacky, LGTM! 🚀

[bee344]

LGTM

[polkadot-js-bot]

This pull request has been automatically locked since there has not been any recent activity after it was closed. Please open a new issue for related bugs.