public static decimal?Min(this OneItemSpecificOrderedEnumerable <decimal?> source)
        {
            if (source.IsDefaultValue())
            {
                throw CommonImplementation.Uninitialized(nameof(source));
            }

            return(source.Item);
        }
        public bool SequenceEqual(OneItemSpecificOrderedEnumerable <TItem> second)
        {
            if (IsDefaultValue())
            {
                throw CommonImplementation.Uninitialized("first");
            }
            if (second.IsDefaultValue())
            {
                throw CommonImplementation.Uninitialized(nameof(second));
            }

            return(EqualityComparer <TItem> .Default.Equals(default(TItem), second.Item));
        }