feat: refund gas to should never be set to address(0)

src/IncentivizedMessageEscrow.sol

@@ -156,6 +156,7 @@ abstract contract IncentivizedMessageEscrow is IIncentivizedMessageEscrow, Bytes
         bytes calldata message,
         IncentiveDescription calldata incentive
     ) checkBytes65Address(destinationAddress) external payable returns(uint256 gasRefund, bytes32 messageIdentifier) {
+        if (incentive.refundGasTo == address(0)) revert RefundGasToIsZero();
         // Check that the application has set a destination implementation
         bytes memory destinationImplementation = implementationAddress[msg.sender][destinationIdentifier];
         // Check that the length is not 0.

src/interfaces/IMessageEscrowErrors.sol

@@ -18,4 +18,5 @@ interface IMessageEscrowErrors {
     error InvalidImplementationAddress();  // c970156c
     error IncorrectValueProvided(uint128 expected, uint128 actual); // 0b52a60b
     error ImplementationAddressAlreadySet(bytes currentImplementation); // dba47850
+    error RefundGasToIsZero(); // 6a1a6afe
 }

test/IncentivizedMessageEscrow/escrowMessage/refundGasTo.t.sol

@@ -0,0 +1,20 @@
+// SPDX-License-Identifier: UNLICENSED
+pragma solidity ^0.8.13;
+
+import "forge-std/Test.sol";
+import { TestCommon } from "../../TestCommon.t.sol";
+
+contract EscrowInformationTest is TestCommon {
+    function test_error_refund_gas_to_0() public {
+        IncentiveDescription storage incentive = _INCENTIVE;
+        incentive.refundGasTo = address(0);
+        vm.expectRevert();
+        (, bytes32 messageIdentifier) = escrow.submitMessage{value: _getTotalIncentive(_INCENTIVE)}(
+            bytes32(uint256(0x123123) + uint256(2**255)),
+            _DESTINATION_ADDRESS_THIS,
+            _MESSAGE,
+            incentive
+        );
+    }
+
+}