Return null if order was not found (#83)

src/datasources/order-api.ts

@@ -118,7 +118,9 @@ export class OrderAPI extends BaseSQLDataSource {
       .orderBy('id')
       .first()
       .cache(MINUTE)
-      .then((row) => this.createOrderFromRow(row));
+      .then((row) => {
+        return row ? this.createOrderFromRow(row) : null;
+      });
   }
 
   async getOrderRowFieldMapping(): Promise<any> {