Description
The ConnextRouter does not check, in the _crossTransfer(...) and _crossTransferWithCalldata(...) functions, if the receiver and routerByDomain[destDomain] equal address(0). This should revert anyway because the Connext contract reverts if _to is address(0), but it's safer to make this additional check.
Recommendation
Check if the address is 0.
Status
Addressed here: Fujicracy/fuji-v2#632