Change the output error message back to use OpenSearchException in the cause chain (#5081)

Signed-off-by: Xue Zhou <[email protected]>

Author: xuezhou25

CHANGELOG.md

@@ -129,6 +129,8 @@ Inspired from [Keep a Changelog](https://keepachangelog.com/en/1.0.0/)
 - Refactored BalancedAllocator.Balancer to LocalShardsBalancer ([#4761](https://github.com/opensearch-project/OpenSearch/pull/4761))
 - Fail weight update when decommission ongoing and fail decommission when attribute not weighed away ([#4839](https://github.com/opensearch-project/OpenSearch/pull/4839))
 - Skip SymbolicLinkPreservingTarIT when running on Windows ([#5023](https://github.com/opensearch-project/OpenSearch/pull/5023))
+- Change the output error message back to use OpenSearchException in the cause chain. ([#5081](https://github.com/opensearch-project/OpenSearch/pull/5081))
+
 ### Deprecated
 ### Removed
 - Remove deprecated code to add node name into log pattern of log4j property file ([#4568](https://github.com/opensearch-project/OpenSearch/pull/4568))

server/src/main/java/org/opensearch/OpenSearchException.java

@@ -588,7 +588,7 @@ public static void generateFailureXContent(XContentBuilder builder, Params param
                 }
                 t = t.getCause();
             }
-            builder.field(ERROR, ExceptionsHelper.summaryMessage(e));
+            builder.field(ERROR, ExceptionsHelper.summaryMessage(t != null ? t : e));
             return;
         }