whatever.ThrowIfNull(nameof(whatever));

ThrowIfNullExtension.cs

namespace System
{
    public static class ThrowIfNullExtension
    {
        // whatever.ThrowIfNull(nameof(whatever));
        [System.Diagnostics.DebuggerStepThrough]
        public static void ThrowIfNull<T>(this T o, string paramName)
            where T : class
        {
            if (o == null)
            {
                throw new ArgumentNullException(paramName);
            }
        }
    }
}