how can i make the loop restart when i press enter?

Im learning C#, and i want to repeat part of my code, if person types not a digit. SO, if person types a letter, everything seems fine, and the loop repeats. But, if the person just click enter, program breaks. First loop works correct, if you click enter, it starts again, but the seond, idk why, but it recongises enter(nothing) as true. Because of this, my formula cant multiply nothing, and i get an error. So, if the bool think that nothing IS a digit, how can i fix this? ( the problem is in first case ).

using System;
using System.Text;

class Geeks
{

    // 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($"Kilo of bananas costs {BananaKgPrice} euros, kilo watermelons {WatermelonKgPrice} euros");
        bool loopBreakBuyChoice = true;
        while (loopBreakBuyChoice)
        {
            Console.WriteLine("What do you want to buy? 1 - banans, 2 - watermelons");
            BuyChoice = Console.ReadLine();
            switch (BuyChoice)
            {
                case "1":
                    loopBreakBuyChoice = false;
                    Console.WriteLine($"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
                        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;
            }

        }
    }
}

I alredy tried to fix my problem here, but i did some problems in my post, so it was closed. Re-trying to make this post, and fix my problem.

>Solution :

If you press enter without entering anything Console.ReadLine will return an empty string. Enumerable.All is implemented that it returns …

true if every element of the source sequence passes the test in the
specified predicate, or if the sequence is empty; otherwise, false.

So i think this fixes the issue:

bool DigitsBanana = !string.IsNullOrEmpty(bananas) && bananas.All(char.IsDigit);

Another approach would be to use int.TryParse because you are actually trying to parse the banana-count:

int bananaCount = 0;
while (true)
{
    Console.WriteLine("How much bananas do you want to buy?");
    if (int.TryParse(Console.ReadLine(), out int count))
    {
        bananaCount = count;
        break;
    }  

    Console.WriteLine("Please insert AMOUNT of bananas.");                 
}

price = bananaCount * Convert.ToDouble(bananaWeight) / Convert.ToDouble(kg) * Convert.ToDouble(BananaKgPrice), 2);