Linq ArgumentException When the Values Change

[rhornjr]

The below code fails with this exception:
System.ArgumentException: At least one object must implement IComparable.

However, if you change this line...
calendarDurations.Add(30);
... to use this...
calendarDurations.Add(14);
... it works.

So it appears the order, or a specfic number matters. This was done on dotnetfiddle.net with .NET 4.7.2 and .NET 6.

using System;
using System.Collections.Generic;
using System.Linq;
			
public class Program
{
	public static void Main()
	{
		var calendarDurations = new List<double>();
		
		calendarDurations.Add(14);
		calendarDurations.Add(14);
		calendarDurations.Add(30);
		calendarDurations.Add(30);
		calendarDurations.Add(7);

		// Get the duration that appears most often. If a tie, take the higher number.
		var max = calendarDurations
			.GroupBy(x => x)
			.Select(x => new { num = x, count = x.Count() })
			.OrderByDescending(g => g.count)
			.ThenByDescending(g => g.num)
			.Select(g => g.num)
			.First();

		int calendaryDuration = (int)max.Key;
		
		Console.WriteLine(calendaryDuration);
	}
}

Stack trace:
Unhandled exception. System.ArgumentException: At least one object must implement IComparable.
at System.Collections.Comparer.Compare(Object a, Object b)
at System.Collections.Generic.ObjectComparer1.Compare(T x, T y) at System.Linq.CachingComparer2.Compare(TElement element, Boolean cacheLower)
at System.Linq.CachingComparerWithChild2.Compare(TElement element, Boolean cacheLower) at System.Linq.OrderedEnumerable1.TryGetFirst(Boolean& found)
at System.Linq.Enumerable.SelectIPartitionIterator2.TryGetFirst(Boolean& found) at System.Linq.Enumerable.TryGetFirst[TSource](IEnumerable1 source, Boolean& found)
at System.Linq.Enumerable.First[TSource](IEnumerable`1 source)
at Program.Main()
Command terminated by signal 6

[rhornjr]

Figured it out.