Dankann

using System.Collections;
using System.Collections.Generic;
using System;

public static class ListExtensions
{
    public static List<T> AddUnique<T>(this List<T> list, T item)
    {
        if(!list.Contains(item))
            list.Add(item);

Dankann

using System;
using System.Threading;
using System.Threading.Tasks;

public static class TaskExtensions
{
    public static async void FireAndForgetAsync(this Task task)
    {
        try
        {