fix: check address code length + tests

src/JBBuybackHook.sol

@@ -560,12 +560,15 @@ contract JBBuybackHook is ERC165, JBPermissioned, IJBBuybackHook {
         // Get a reference to the pool that'll be used to make the swap.
         IUniswapV3Pool pool = poolOf[projectId][address(terminalToken)];
 
-        // Make sure the pool exists.
+        // Make sure the pool exists, if not, return an empty quote.
+        if (address(pool).code.length == 0) return 0;
+
+        // If there is a contract at the address, try to get the pool's slot 0.
         try pool.slot0() returns (uint160, int24, uint16, uint16, uint16, uint8, bool unlocked) {
             // If the pool hasn't been initialized, return an empty quote.
             if (!unlocked) return 0;
         } catch {
-            // If the address is invalid, or if the pool has not been deployed yet, return an empty quote.
+            // If the address is invalid, return an empty quote.
             return 0;
         }
 

test/Unit.t.sol

@@ -326,6 +326,35 @@ contract Test_BuybackHook_Unit is Test {
     /// minting
     /// from the terminal.
     function test_beforePayRecordedContext_useTwapNonDeployedPool(uint256 tokenCount) public {
+        vm.etch(address(pool), "");
+        assert(address(pool).code.length == 0);
+
+        tokenCount = bound(tokenCount, 1, type(uint120).max);
+
+        // Set the relevant context.
+        beforePayRecordedContext.weight = tokenCount;
+        beforePayRecordedContext.metadata = "";
+
+        // Return values to catch:
+        JBPayHookSpecification[] memory specificationsReturned;
+        uint256 weightReturned;
+
+        // Test: call `beforePayRecordedWith` - notice we don't mock the pool, as the address should remain empty
+        vm.prank(terminalStore);
+        (weightReturned, specificationsReturned) = hook.beforePayRecordedWith(beforePayRecordedContext);
+
+        // No hook specifications should be returned.
+        assertEq(specificationsReturned.length, 0);
+
+        // The weight should be returned unchanged.
+        assertEq(weightReturned, tokenCount);
+    }
+
+    /// @notice Test `beforePayRecordedWith` with a TWAP but an invalid pool address, which should lead to the payment
+    /// minting from the terminal.
+    function test_beforePayRecordedContext_useTwapInvalidPool(uint256 tokenCount) public {
+        vm.etch(address(pool), "12345678");
+
         tokenCount = bound(tokenCount, 1, type(uint120).max);
 
         // Set the relevant context.