fix linter

Author: KirillKurdyukov

src/Ydb.Sdk/src/Driver.cs

@@ -130,7 +130,7 @@ private async Task<Status> DiscoverEndpoints()
         };
 
         var options = GetCallOptions(requestSettings);
-        options.Headers.Add(Metadata.RpcSdkInfoHeader, _sdkInfo);
+        options.Headers?.Add(Metadata.RpcSdkInfoHeader, _sdkInfo);
 
         var response = await client.ListEndpointsAsync(
             request: request,

src/Ydb.Sdk/src/Services/Table/Transaction.cs

@@ -28,7 +28,7 @@ internal Transaction(string txId)
         if (!string.IsNullOrEmpty(proto.Id))
         {
             tx.TxNum = IncTxCounter();
-            logger.LogTrace($"Received tx #{tx.TxNum}");
+            logger?.LogTrace($"Received tx #{tx.TxNum}");
         }
 
         return tx;