implemented generic sanity checks

src/AdvancedOrderEngine.sol

@@ -2,17 +2,50 @@
 pragma solidity 0.8.21;
 
 import {OrderEngine} from "./libraries/OrderEngine.sol";
+import "./AdvancedOrderEngineErrors.sol";
 
 contract AdvancedOrderEngine {
     using OrderEngine for OrderEngine.Order;
 
+    /**
+     * @notice Fills multiple orders by processing the specified orders and clearing prices.
+     *
+     * @param orders An array of order structs representing the orders to be filled.
+     * @param clearingPrices An array of clearing prices that the facilitator is offering to the makers.
+     * @param facilitatorInteractionCalldata The calldata for the facilitator's interaction.
+     * @param facilitatorInteractionTargetContract The address of the facilitator's target contract.
+     */
     function fillOrders(
         OrderEngine.Order[] calldata orders,
         uint256[] calldata clearingPrices,
         bytes calldata facilitatorInteractionCalldata,
         address facilitatorInteractionTargetContract
     ) external {
-        // Perform sanity checks (for example, orders and clearing prices array must have same length, etc)
+        // TBD: max array length check needed? Considering fn will be restricted to operators only
+
+        /** 
+            TBD: no need to check for clearingPrices length to be equal to 0 as if that's the case, txn will revert in subsequent check
+            but should we check for clearingPrices length to be equal to zero explicitly for better error reporting? 
+            Also consider generic error message
+        */
+        // Revert if the orders array length is zero.
+        if (orders.length == 0) {
+            revert EmptyOrdersArray();
+        }
+
+        // Revert if the length of the orders array does not match the clearing prices array.
+        if (orders.length != clearingPrices.length) {
+            revert ArraysLengthMismatch(orders.length, clearingPrices.length);
+        }
+
+        // Revert if the facilitator has provided calldata for its interaction but has provided null target contract address.
+        if (
+            facilitatorInteractionCalldata.length != 0 &&
+            facilitatorInteractionTargetContract == address(0)
+        ) {
+            revert ZeroFacilitatorTargetAddress(); // TBD: use generic error message i.e. ZeroAddress()
+        }
+
         // Loop start
         // Perform order specific sanity checks
         // Verify signatjures

src/AdvancedOrderEngineErrors.sol

@@ -0,0 +1,6 @@
+// SPDX-License-Identifier: MIT
+pragma solidity 0.8.21;
+
+error ArraysLengthMismatch(uint256 ordersArrLen, uint256 clearingPricesArrLen);
+error ZeroFacilitatorTargetAddress();
+error EmptyOrdersArray();