csharp(CS8600)

TheGame12

I'm getting the error CS8600 (Converting null literal or possible null value to non-nullable type.) And I don't know why. Here is a snippet of the code and context:

Random rng = new Random();

        Random dmg = new Random();

        string[] monsters = {"skeleton", "goblin", "zombie"};

        int[] monstersHealth = {3, 2, 5};

        int monsterPicked = rng.Next(0, 3);

        int monsterPickedHealth = monstersHealth[monsterPicked];

        string monsterName = monsters[monsterPicked];

        Console.Write("You adventure down a cave, and find a " + monsterName + " blocking your path!\n");

        Console.Write("What would you like to do?\n Attack, Guard, Run\n");

        string fightCommand = Console.ReadLine();

        Console.Write("You wrote " + fightCommand + "!");

        if (fightCommand == "attack" || fightCommand == "Attack")

        {

            int damage = dmg.Next(1, 4);

            Console.Write("You use your trusty wooden sword to attack the " + monsterName + ".\nYou do " + damage + " damage!\n");

            int result1 = monsterPickedHealth - damage;

            Console.Write("The " + monsterName + " has " + result1 + " health left!");

           

           

        }

Wow that's a lot