Gondi

It is important to validate inputs, even if they only come from trusted addresses, to avoid human error. Specifically, in the following functions arguments could could benefit from additional input validation: 1. Generally, in constructors, address parameters, especially if used to assign immutable variables, should be checked to be unequal to zero. Furthermore, all assignments of global state variable that have matching setters should make use of those setters to leverage the existing input validation. 4. `Leverage.updateMultiSourceLoanAddressFirst()`: Validate that `_newAddress` is non-zero. 5. `Leverage.updateSeaportAddressFirst()`: Validate that `_newAddress` is non-zero. 8. `BaseLoan.updateImprovementMinimum()`: Validate that `_newMinimum` is non-zero to not enable refinances with identical APR. 4. `BaseLoan.updateLiquidationAuctionDuration()`: The function allows the auction duration to be `zero`. Consider adding a minimum check. 3. `BaseLoan.updateImprovementMinimum()`: Validate its input against some minimum values. According to the documentation, these should be `1%` principal amount increase, `1%` interest decrease, or `10%` duration increase. 13. `MultiSourceLoan.setMaxSources()`: Validate that `maxSources` is non-zero and have a reasonable hardcoded upper bound to not cause block gas limit concerns in their processing. 14. `MultiSourceLoan.updateRefinanceInterestFraction()`: Validate that `_newFraction` is lower than `PRECISION.` 1. `AuctionLoanLiquidator.placeBid()`: Validate that `_bid` is greater than zero, as else a bid of zero amount could technically win the auction. 14. `WithCallbacks.addWhitelistedCallbackContract()`: Validate that `_contract` is non-zero and `_tax` is lower than `PRECISION`. 1. `AddressManager._add()`: Validate that `entry` is valid. Otherwise, it would allow `address(0)` to be added to the registry.