adding condition for allowing rcv to be none if close to is set

[barnjamin]

closes #316

This should still raise a useful error in the case that close to is also zero since that is likely user error.

[algochoi]

Looks fine to me

nit: not sure if ZERO_ADDRESS should live in transaction.py or constants.py. I don't have a strong opinion so I'll just leave it as a thought.

[barnjamin]

nit: not sure if ZERO_ADDRESS should live in transaction.py or constants.py. I don't have a strong opinion so I'll just leave it as a thought.

Good point, moved it.

[jasonpaulos]

This seems like a good idea but it does open up a new edge case: what if amount is > 0? In that case the amount gets sent to the receiver (which is the zero address now), and the account balance minus that amount gets sent to the close to address.

Perhaps the condition should be close_remainder_to is not None and not amt?

[jasonpaulos]

To clarify, is this change meant to fix decoding transactions properly from a block, or to let users instantiate transactions in a more useful way?

[barnjamin]

This seems like a good idea but it does open up a new edge case: what if amount is > 0? In that case the amount gets sent to the receiver (which is the zero address now), and the account balance minus that amount gets sent to the close to address.

Good point, I guess your suggestion of checking amt >0 should also be implemented.

To clarify, is this change meant to fix decoding transactions properly from a block, or to let users instantiate transactions in a more useful way?

In this case the bug report I got was when decoding a transaction included in a block where apparently no rcv was set. Locally they can just patch it to set the zero address if it isnt already present

[jasonpaulos]

Thanks for addressing the concerns I raised offline. This looks good, but it would be amazing if you could also add a test to test_unit.py that makes sure calling future_msgpack_decode on a txn where the receiver is the zero address works properly now

[jasonpaulos]

Looks great, thanks