Users/ismayilov ismayil/add delay when message null

src/Agent.Listener/MessageListener.cs

@@ -261,6 +261,9 @@ public async Task<TaskAgentMessage> GetNextMessageAsync(CancellationToken token)
                         Trace.Verbose($"No message retrieved from session '{_session.SessionId}'.");
                     }
 
+                    _getNextMessageRetryInterval = BackoffTimerHelper.GetRandomBackoff(TimeSpan.FromSeconds(5), TimeSpan.FromSeconds(15), _getNextMessageRetryInterval);
+                    Trace.Info("Sleeping for {0} seconds before retrying.", _getNextMessageRetryInterval.TotalSeconds);
+                    await HostContext.Delay(_getNextMessageRetryInterval, token);
                     continue;
                 }