Fix "Failed to initialize plugin" NullReferenceException in Oxide plugins

using System;
using System.Collections.Generic;
using Newtonsoft.Json;
using Oxide.Core;
using UnityEngine;

namespace Oxide.Plugins
{
    [Info("ServerRewards", "RustPluginGenerator", "1.0.0")]
    [Description("Gives players points they can spend with a chat command")]
    public class ServerRewards : RustPlugin
    {
        private class StoredData
        {
            public Dictionary<string, int> Points = new Dictionary<string, int>();
        }

        private class PluginConfig
        {
            [JsonProperty("Points per message")]
            public int PointsPerMessage = 5;

            [JsonProperty("Welcome message")]
            public string Welcome = "Welcome, {0}!";
        }

        private PluginConfig config;
        private StoredData data;

        private void Init()
        {
            // Config and player lists are not ready here. Register nothing that needs them.
        }

        private void OnServerInitialized()
        {
            if (config == null || string.IsNullOrEmpty(config.Welcome)) return;

            foreach (var player in BasePlayer.activePlayerList)
            {
                if (player == null || !player.IsConnected) continue;
                player.ChatMessage(string.Format(config.Welcome, player.displayName));
            }
        }

        private void Loaded()
        {
            data = Interface.Oxide.DataFileSystem.ReadObject<StoredData>(Name);
            if (data == null) data = new StoredData();
        }

        protected override void LoadDefaultConfig() => config = new PluginConfig();

        protected override void LoadConfig()
        {
            base.LoadConfig();
            try
            {
                config = Config.ReadObject<PluginConfig>();
                if (config == null) throw new System.Exception();
            }
            catch
            {
                PrintWarning("Configuration file is invalid, using defaults");
                LoadDefaultConfig();
            }
            SaveConfig();
        }

        protected override void SaveConfig() => Config.WriteObject(config);

        protected override void LoadDefaultMessages()
        {
            lang.RegisterMessages(new Dictionary<string, string>
            {
                ["Points"] = "You have {0} points."
            }, this);
        }

        private void Unload()
        {
            if (data != null) Interface.Oxide.DataFileSystem.WriteObject(Name, data);
            data = null;
        }

        [ChatCommand("points")]
        private void CmdPoints(BasePlayer player, string command, string[] args)
        {
            if (player == null || data == null) return;
            int points;
            if (!data.Points.TryGetValue(player.UserIDString, out points)) points = 0;
            SendReply(player, lang.GetMessage("Points", this, player.UserIDString), points);
        }
    }
}