how to make the code not break when the enter key is pressed?

So, im learing C# right now, and i was making my console program, which sells you some fruits. with the help of loop, I made it so that if a person enters a non-digit, then the loop starts over. But it turns out, if i type nothing and just press enter, my code gets an error. What should I do in such a situation? How can I change the code?

// Main Method
public static void Main()
{
    //buy
    float kg = 1000;
    string bananas;
    float BananaKgPrice = 1.69f;
    float bananaWeight = 200;
    float WatermelonKgPrice = 3.29f;
    double price;
    string BuyChoice;

    Console.WriteLine("Welcome to our shop! We sell bananas and watermelons.");
    Console.WriteLine($"Kilo of bananas costs {BananaKgPrice} euros, kilo watermelons {WatermelonKgPrice} euros");
    bool loopBreakBuyChoice = true;
    while (loopBreakBuyChoice)
    {
        Console.WriteLine("What do you want to buy? 1 - bananas, 2 - watermelons");
        BuyChoice = Console.ReadLine();
        switch (BuyChoice)
        {
            case "1":
                loopBreakBuyChoice = false;
                Console.WriteLine($"Price of bananas for kilo.: {BananaKgPrice} euro");
                bool loopBreakBananaDigits = true;
                while (loopBreakBananaDigits)
                {
                    Console.WriteLine("How much bananas do you want to buy?");
                    bananas = Console.ReadLine();//press enter +digit
                    ConsoleKeyInfo key;
                    key = Console.ReadKey(true);
                    if (key.Key == ConsoleKey.Enter)
                    {

                    }
                    else
                    {
                        bool DigitsBanana = bananas.All(char.IsDigit);
                        if (DigitsBanana != true)
                        {
                            loopBreakBananaDigits = true;
                            Console.WriteLine("Please insert AMOUNT of bananas.");
                        }

                        if (DigitsBanana == true)
                        {
                            loopBreakBananaDigits = false;
                            loopBreakBuyChoice = false;
                            price = Math.Round(Convert.ToDouble(bananas) * Convert.ToDouble(bananaWeight) / Convert.ToDouble(kg) * Convert.ToDouble(BananaKgPrice), 2);
                        }
                    }
                }

                break;
         }         
    }
}