noticket: Fix NPE on YdbRepositoryTransaction.trace() for read-only queries

Author: nvamelichev

repository-ydb-v2/src/main/java/tech/ydb/yoj/repository/ydb/YdbRepositoryTransaction.java

@@ -652,7 +652,7 @@ private static String debugResult(Object result) {
 
     private void trace(@NonNull Statement<?, ?> statement, Object params, Throwable thrown, Object results) {
         var txId = firstNonNullTxId;
-        var sessionId = session.getId();
+        var sessionId = session == null ? null : session.getId();
         var tablespace = repo.getTablespace();
         log.trace("{}", new StatementTraceEvent(
                 statement,