return null TxControl on Completed Transaction

Author: KirillKurdyukov

src/Ydb.Sdk/src/Ado/YdbTransaction.cs

@@ -13,9 +13,11 @@ public sealed class YdbTransaction : DbTransaction
     internal bool Completed { get; set; }
     internal bool Failed { get; set; }
 
-    internal TransactionControl TransactionControl => TxId == null
-        ? new TransactionControl { BeginTx = _txMode.TransactionSettings() }
-        : new TransactionControl { TxId = TxId };
+    internal TransactionControl? TransactionControl => Completed || Failed
+        ? null
+        : TxId == null
+            ? new TransactionControl { BeginTx = _txMode.TransactionSettings() }
+            : new TransactionControl { TxId = TxId };
 
     internal YdbTransaction(YdbConnection ydbConnection, TxMode txMode)
     {

src/Ydb.Sdk/tests/Ado/YdbExceptionTests.cs

@@ -57,7 +57,8 @@ public async Task IsTransient_WhenAborted_ReturnTrueAndMakeEmptyRollback()
         {
             CommandText = $"DROP TABLE {bankTable}"
         }.ExecuteNonQueryAsync();
-        Assert.Equal("Status: NotFound", Assert.Throws<YdbException>(() => ydbCommand.Transaction.Commit()).Message);
+        Assert.Equal("This YdbTransaction has completed; it is no longer usable",
+            Assert.Throws<InvalidOperationException>(() => ydbCommand.Transaction.Commit()).Message);
 
         await ydbCommand.Transaction!.RollbackAsync();
         Assert.Equal("This YdbTransaction has completed; it is no longer usable",