Fix OrderWatcher race-condition bug

packages/order-watcher/CHANGELOG.json

@@ -1,4 +1,13 @@
 [
+    {
+        "version": "4.0.7",
+        "changes": [
+            {
+                "note": "Fix race-condition bug due to async callback modifying shared state",
+                "pr": 1789
+            }
+        ]
+    },
     {
         "version": "4.0.6",
         "changes": [

packages/order-watcher/src/order_watcher/order_watcher.ts

@@ -493,6 +493,9 @@ export class OrderWatcher {
     private async _emitRevalidateOrdersAsync(orderHashes: string[], transactionHash?: string): Promise<void> {
         for (const orderHash of orderHashes) {
             const signedOrder = this._orderByOrderHash[orderHash];
+            if (signedOrder === undefined) {
+                continue;
+            }
             // Most of these calls will never reach the network because the data is fetched from stores
             // and only updated when cache is invalidated
             const orderState = await this._orderStateUtils.getOpenOrderStateAsync(signedOrder, transactionHash);