Submitted by cmichel
Some tokens (like USDT) dont correctly implement the EIP20 standard and their transfer/transferFrom functions return void, instead of a success boolean. Calling these functions with the correct EIP20 function signatures will always revert. See CompoundToNotionalV2.notionalCallbacks IERC20(underlyingToken).transferFrom call.
Tokens that dont correctly implement the latest EIP20 spec, like USDT, will be unusable in the protocol as they revert the transaction because of the missing return value.
The fact that there is a cToken with USDT as the underlying this issue directly applies to the protocol.
We recommend using OpenZeppelins SafeERC20 versions with the safeTransfer and safeTransferFrom functions that handle the return value check as well as non-standard-compliant tokens.
jeffywu (Notional) confirmed
