core: add a comment for error return of nil

[wangjingcun]

According to the comments and code logic, the err here should be handled by the upper layer GetTransaction

Add a comment for error return of nil

[MariusVanDerWijden]

I think the err should not be passed up.
GetTransactionLookup should return an error if a transaction can not be determined to be found or not.
Doing so allows callers to periodically re-request these transaction if needed.
The only cases that bc.TxIndexProgress() errors is if the transaction indexing is not started or stopped already.
In both cases the transaction will not be found in the future, so we correctly return nil imo.
We could add a comment for this though

[wangjingcun]

I think the err should not be passed up. GetTransactionLookup should return an error if a transaction can not be determined to be found or not. Doing so allows callers to periodically re-request these transaction if needed. The only cases that bc.TxIndexProgress() errors is if the transaction indexing is not started or stopped already. In both cases the transaction will not be found in the future, so we correctly return nil imo. We could add a comment for this though

Thank you for your review. Do you have any good suggestions for adding to the review? I'd be happy to add them.

[MariusVanDerWijden]

SGTM

[holiman]

lgtm