fix(transfer): allow zero transfers

[Rubilmax]

• Fixes Transfer reverts on zero amount #297

[MerlinEgalite]

Should we add a comments since it's a bit different from the standard that we use in other bundlers

[julien-devatom]

The problem is that an erc20 can revert on 0 transfer. We have a specific usecase to transfer(0), for slippage undertaken amount (if we reach the slippage tolerance). So I would suggest to have an early return and to not call the safeTransfer is 0, or to add a skim function that is returning on 0 amount.

[Jean-Grimal]

Maybe we should add a return before the call to the token contract if the amount is zero

[Rubilmax]

The problem is that an erc20 can revert on 0 transfer. We have a specific usecase to transfer(0), for slippage undertaken amount (if we reach the slippage tolerance). So I would suggest to have an early return and to not call the safeTransfer is 0, or to add a skim function that is returning on 0 amount.

if the token is strictly EIP-20 compliant it shouldn't, do you have counter-examples in mind?

EDIT: however, for efficiency reason, there's indeed no reason to call the ERC20

[julien-devatom]

IMO, we have to reference somewhere that the 0 amount is not calling the transfer (and thus not triggering a Transfer event). This is a specific behavior different from the one defined by the EIP20, where the end user can expect to have a Transfer event with a 0 amount

[MerlinEgalite]

why merging it?