Support update expressions in single request update

Author: anasatirbasa

services-custom/dynamodb-enhanced/src/main/java/software/amazon/awssdk/enhanced/dynamodb/internal/operations/UpdateItemOperation.java

@@ -289,9 +289,8 @@ private Expression generateUpdateExpressionIfExist(
         Either<UpdateItemEnhancedRequest<T>, TransactUpdateItemEnhancedRequest<T>> request) {
 
         UpdateExpression requestUpdateExpression =
-            request.map(r -> Optional.ofNullable(r.updateExpression()),
-                        r -> Optional.ofNullable(r.updateExpression()))
-                   .orElse(null);
+            request.left().map(UpdateItemEnhancedRequest::updateExpression)
+                   .orElseGet(() -> request.right().map(TransactUpdateItemEnhancedRequest::updateExpression).orElse(null));
 
         UpdateExpressionResolver updateExpressionResolver =
             UpdateExpressionResolver.builder()