Incorrect type behaviour in TransactionResponse

[th0masb]

Describe the bug
A clear and concise description of what the bug is.

The Transaction/TransactionResponse interfaces have misleading and incorrect types. The interface indicates the to field should have type string | undefined however there is a transaction hash which returns null for this field.

Reproduction steps
Please include code snippets, with console.log output, any contract ABI, contract address, network and the full error.

const tx = await provider.getTransaction("0xd9489355786845fcf93256bfb63472ca7ee58b6dfde7ccc55e9bfa60862202a3")
if (tx.to !== undefined) {
  console.log(tx.to.toLowerCase()) // This compiles but goes boom at runtime
}

[ricmoo]

The types in v5 do not distinguish between null and undefined, so you should use ==. In v6 this will be more explicitly typed. :)