Passing null instead of credentials

Hi Alex,

Shouldn't
```
		public ZyanConnection(string serverUrl, Hashtable credentials, bool autoLoginOnExpiredSession, bool keepSessionAlive)
			: this(serverUrl, ClientProtocolSetup.GetClientProtocol(serverUrl), null, autoLoginOnExpiredSession, true)
		{
		}
```
in ZyanConnection.cs be passing `credentials` and not `null`?

Greetings
Alex
