walletrpc SendOutputs fails to attach zero value outputs

[alexbosworth]

Background

When sending a transaction to specific output scripts using SendOutputs in walletrpc, specifying output values that are 0 results in an invalid transaction that gets rejected on broadcast due to it being formed without inputs.

Zero value outputs are valid by consensus rules and standard by p2p policy rules when used with an OP_RETURN output script.

Your environment

• lnd 0.12.1-beta

Steps to reproduce

Using a wallet with on-chain funds, send funds using SendOutputs specifying a 0-value OP_RETURN

Expected behavior

The 0 value single output should be created and sent

Actual behavior

An error is returned from the chain daemon indicating an invalid transaction was received transaction has no inputs

Specifying a value of 1 for the OP_RETURN will result in a successful transaction

[jacohend]

I'm not having this particular issue when using SendOutputs to create OP_RETURNS- I'm using lnd 0.12.1-beta compiled with latest neutrino master. Here's the code.

[jacohend]

I will note, however, that we have had occasional strange issues with this. @Roasbeef mentioned the potential for this in #4150 (comment)