Every time i try to call SendMessage, it puts out this error 

Failed to call hook 'OnPlayerChat' on plugin 'DiscordChat v0.0.1' (NullReferenceException: Object reference not set to an instance of an object) at Oxide.Plugins.DiscordChat.OnPlayerChat (BasePlayer player, System.String message) [0x00000] in <c6002dba396d40f0a92b2690375d172e>:0 at Oxide.Plugins.DiscordChat.DirectCallHook (System.String name, System.Object& ret, System.Object[] args) [0x00032] in <c6002dba396d40f0a92b2690375d172e>:0 at Oxide.Plugins.CSharpPlugin.InvokeMethod (Oxide.Core.Plugins.HookMethod method, System.Object[] args) [0x00079] in <31122a27a2414cd799150f8677cf39d4>:0 at Oxide.Core.Plugins.CSPlugin.OnCallHook (System.String name, System.Object[] args) [0x000d8] in <c2afd8354b8b4f3ca451cf5a1aa111c3>:0 at Oxide.Core.Plugins.Plugin.CallHook (System.String hook, System.Object[] args) [0x00060] in <c2afd8354b8b4f3ca451cf5a1aa111c3>:0

The code in my plugin is this. 

[PluginReference] private Plugin Discord;
private static DiscordChat ins;

private void OnPlayerChat(BasePlayer player, string message, Chat.ChatChannel channel)
{
ins.Discord?.Call("SendMessage", message);
}

Whats causing this error?