Assets/MFPS/Scripts/Network/bl_chatRoom.cs(78,14): error CS0019: Operator `!=' cannot be applied to operands of type `PhotonMessageInfo' and `null'

using UnityEngine;
using System.Collections;
using System.Collections.Generic;
using UnityEngine.UI;

public class bl_ChatRoom : bl_PhotonHelper {

public GUISkin m_Skin;
[Space(5)]
public Text ChatText;
public bool IsVisible = true;
public bool WithSound = true;
public int MaxMsn = 7;
public List<string> messages = new List<string>();
private string inputLine = "";
[Space(5)]
public AudioClip MsnSound;

public static readonly string ChatRPC = "Chat";
private float m_alpha = 2f;
private bool isChat = false;

void Start()
{
	Refresh();
}

public void OnGUI()
{
	if (ChatText == null)
		return;

	if (m_alpha > 0.0f && !isChat)
	{
		m_alpha -= Time.deltaTime / 2;
	}
	else if (isChat)
	{
		m_alpha = 10;
	}

	Color t_color = ChatText.color;
	t_color.a = m_alpha;
	ChatText.color = t_color;

	GUI.skin = m_Skin;
	GUI.color = new Color(1, 1, 1, m_alpha);
	if (!this.IsVisible || PhotonNetwork.connectionStateDetailed != ClientState.Joined)
	{
		return;
	}

	if (Event.current.type == EventType.KeyDown && (Event.current.keyCode == KeyCode.KeypadEnter || Event.current.keyCode == KeyCode.Return))
	{
		if (!string.IsNullOrEmpty(this.inputLine) && isChat && bl_UtilityHelper.GetCursorState)
		{
			this.photonView.RPC("Chat", PhotonTargets.All, this.inputLine);
			this.inputLine = "";
			GUI.FocusControl("");
			isChat = false;
			return; // printing the now modified list would result in an error. to avoid this, we just skip this single frame
		}
		else if (!isChat && bl_UtilityHelper.GetCursorState)
		{
			GUI.FocusControl("ChatInput");
			isChat = true;
		}
		else
		{
			if (isChat)
			{
				Closet();
			}
		}
	}

	GUI.SetNextControlName("");
	GUILayout.BeginArea(new Rect(Screen.width / 2 - 150, Screen.height - 35, 300, 50));
	GUILayout.BeginHorizontal();
	GUI.SetNextControlName("ChatInput");
	inputLine = GUILayout.TextField(inputLine);
	if (GUILayout.Button("Send", "box", GUILayout.ExpandWidth(false)))
	{
		this.photonView.RPC("Chat", PhotonTargets.All, this.inputLine);
		this.inputLine = "";
		GUI.FocusControl("");
	}
	GUILayout.EndHorizontal();
	GUILayout.EndArea();

}

void Closet()
{
	isChat = false;
	GUI.FocusControl("");
}
/// <summary>
/// Sync Method
/// </summary>
/// <param name="newLine"></param>
/// <param name="mi"></param>
[RPC]
public void Chat(string newLine, PhotonMessageInfo mi)
{
	m_alpha = 7;
	string senderName = "anonymous";

	if (mi != null && mi.sender != null)
	{
		if (!string.IsNullOrEmpty(mi.sender.name))
		{
			senderName = mi.sender.name;
		}
		else
		{
			senderName = "player " + mi.sender.ID;
		}
	}

	this.messages.Add("[" + senderName + "]: " + newLine);
	if (MsnSound != null && WithSound)
	{
		GetComponent<AudioSource>().PlayOneShot(MsnSound);
	}
	if (messages.Count > MaxMsn)
	{
		messages.RemoveAt(0);
	}

	ChatText.text = "";
	foreach (string m in messages)
		ChatText.text += m + "

";
}
///


/// Local Method
///

///
public void AddLine(string newLine)
{
m_alpha = 7;
this.messages.Add(newLine);
if (messages.Count > MaxMsn)
{
messages.RemoveAt(0);
}
}

public void Refresh()
{
	ChatText.text = "";
	foreach (string m in messages)
		ChatText.text += m + "

";
}
}

change this line 41 :

     **if (!this.IsVisible || PhotonNetwork.connectionStateDetailed != ClientState.Joined)**

into this :

     ***if (!this.IsVisible || PhotonNetwork.connectionStateDetailed != PeerState.Joined)***