Объединение в одну коллекцию

using System;
using System.Collections.Generic;

namespace CSLight
{
    internal class Program
    {
        static void Main()
        {
            List<string> joiningData = new List<string>();

            string[] firstArray = new string[12];
            string[] secondArray = new string[10];

            Console.CursorVisible = false;

            AddData(firstArray);
            AddData(secondArray);

            OutputArray(firstArray);

            Console.WriteLine("\n");

            OutputArray(secondArray);

            Console.ReadKey();

            JoinData(joiningData, firstArray);
            JoinData(joiningData, secondArray);

            Console.WriteLine("\n");

            foreach (var element in joiningData)
            {
                Console.Write($"{element} ");
            }

            Console.ReadKey();
            Console.Clear();
        }

        static void AddData(string[] array)
        {
            int minNumber = 0;
            int maxNumber = 25;

            Random random = new Random();

            for (int i = 0; i < array.Length; i++)
            {
                array[i] = Convert.ToString(random.Next(minNumber, maxNumber));
            }
        }

        static void JoinData(List<string> joiningData, string[] array)
        {
            for (int i = 0; i < array.Length; i++)
            {
                if (joiningData.Contains(array[i]) == false)
                {
                    joiningData.Add(array[i]);
                }
            }
        }

        static void OutputArray(string[] array)
        {
            for (int i = 0; array.Length > i; i++)
            {
                Console.Write($"{array[i]} ");
            }
        }
    }
}