use single method for status code

Author: zeitlinger

instrumentation/elasticsearch/elasticsearch-rest-common-5.0/library/src/main/java/io/opentelemetry/instrumentation/elasticsearch/rest/common/v5_0/internal/ElasticsearchDbAttributesGetter.java

@@ -101,5 +101,6 @@ public String getResponseStatus(@Nullable Response response, @Nullable Throwable
       return DbResponseStatusUtil.httpStatusToResponseStatus(
           response.getStatusLine().getStatusCode());
     }
+    return null;
   }
 }

instrumentation/opensearch/opensearch-rest-common/javaagent/src/main/java/io/opentelemetry/javaagent/instrumentation/opensearch/rest/OpenSearchRestAttributesGetter.java

@@ -59,5 +59,6 @@ public String getResponseStatus(@Nullable Response response, @Nullable Throwable
       return DbResponseStatusUtil.httpStatusToResponseStatus(
           response.getStatusLine().getStatusCode());
     }
+    return null;
   }
 }