Code Throws unexpected Exception

I've done my code for the challenge, but when I try to check it, it gives me this error:

System.ArgumentNullException: Value cannot be null. Parameter name: String at System.Number.StringToNumber (System.String str, System.Globalization.NumberStyles options, System.Number+NumberBuffer& number, System.Globalization.NumberFormatInfo info, System.Boolean parseDecimal) [0x00054] in /builddir/build/BUILD/mono-4.8.1/mcs/class/referencesource/mscorlib/system/number.cs:1074 at System.Number.ParseInt32 (System.String s, System.Globalization.NumberStyles style, System.Globalization.NumberFormatInfo info) [0x00014] in /builddir/build/BUILD/mono-4.8.1/mcs/class/referencesource/mscorlib/system/number.cs:745 at System.Int32.Parse (System.String s) [0x00000] in /builddir/build/BUILD/mono-4.8.1/mcs/class/referencesource/mscorlib/system/int32.cs:120 at Treehouse.CodeChallenges.Program.Main () [0x00010] in <35630bf8787845348d3ead5c0cbbc3e4>:0 at MonoTester.Run () [0x000d5] in /workdir/MonoTester.cs:93

What happened here?

using System;

namespace Treehouse.CodeChallenges
{
    class Program
    {
        static void Main()
        {
            while(true)
            {
                try
                {
                    Console.Write("Enter the number of times to print \"Yay!\": ");
                    string input = Console.ReadLine();

                    int count = int.Parse(input);

                    int i = 0;
                    while(i < count)
                    {
                        i += 1;   
                        Console.WriteLine("Yay!");
                    }
                }
                catch(FormatException)
                {
                   Console.WriteLine("You must enter a whole number.");
                   continue;
                }
            }
        }
    }
}