try IERC721Receiver(to).onERC721Received(_msgSender(), from, tokenId, data) returns (bytes4 retval) {
// test/paprController/OnERC721ReceivedTest.sol

function testSafeTransferByOperator_AUDIT() public {
    address operator = address(0x12345);

    vm.prank(borrower);
    nft.setApprovalForAll(operator, true);

    vm.prank(operator);
    nft.safeTransferFrom(borrower, address(controller), collateralId, abi.encode(safeTransferReceivedArgs));

    // NFT was deposited to the operator's vault.
    IPaprController.VaultInfo memory vaultInfo = controller.vaultInfo(operator, collateral.addr);
    assertEq(vaultInfo.count, 1);

    // Borrower has 0 tokens in collateral.
    vaultInfo = controller.vaultInfo(borrower, collateral.addr);
    assertEq(vaultInfo.count, 0);
}

function testSafeTransferByApproved_AUDIT() public {
    address approved = address(0x12345);

    vm.prank(borrower);
    nft.approve(approved, collateralId);

    vm.prank(approved);
    nft.safeTransferFrom(borrower, address(controller), collateralId, abi.encode(safeTransferReceivedArgs));

    // NFT was deposited to the approved address's vault.
    IPaprController.VaultInfo memory vaultInfo = controller.vaultInfo(approved, collateral.addr);
    assertEq(vaultInfo.count, 1);

    // Borrower has 0 tokens in collateral.
    vaultInfo = controller.vaultInfo(borrower, collateral.addr);
    assertEq(vaultInfo.count, 0);
}
--- a/src/PaprController.sol
+++ b/src/PaprController.sol
@@ -156,7 +156,7 @@ contract PaprController is
     /// @param _id the id of the NFT
     /// @param data encoded IPaprController.OnERC721ReceivedArgs
     /// @return selector indicating succesful receiving of the NFT
-    function onERC721Received(address from, address, uint256 _id, bytes calldata data)
+    function onERC721Received(address, address from, uint256 _id, bytes calldata data)
         external
         override
         returns (bytes4)
