Select list enumerable extensions

EnumerableExtensions.cs

public static class EnumerableExtensions
{
  public static IEnumerable<SelectListItem> ToSelectListItems<T>(this IEnumerable<T> items, Func<T, string> name, Func<T, string> value, string selectedValue)
  {
    return items.ToSelectListItems(name, value, selectedValue, false);
  }

  public static IEnumerable<SelectListItem> ToSelectListItems<T>(this IEnumerable<T> items, Func<T, string> name, Func<T, string> value, string selectedValue, bool includeNotApplicable, string notApplicableValue = "", string notApplicableText = "(Not Applicable)")
  {
    return items.ToSelectListItems(name, value, x => value(x) == selectedValue, includeNotApplicable, notApplicableValue, notApplicableText);
  }

  public static IEnumerable<SelectListItem> ToSelectListItems<T>(this IEnumerable<T> items, Func<T, string> name, Func<T, string> value, Func<T, bool> isSelected)
  {
    return items.ToSelectListItems(name, value, isSelected, false);
  }

  public static IEnumerable<SelectListItem> ToSelectListItems<T>(this IEnumerable<T> items, Func<T, string> name, Func<T, string> value, Func<T, bool> isSelected, bool includeNotApplicable, string notApplicableValue = "", string notApplicableText = "(Not Applicable)")
  {
    if (includeNotApplicable)
    {
      var returnItems = new List<SelectListItem>
                          {
                            new SelectListItem
                              {
                                Text = notApplicableText,
                                Value = notApplicableValue,
                                Selected = false
                              }
                          };

      if (items != null)
      {
        returnItems.AddRange(items.Select(item => new SelectListItem
                              {
                                Text = name(item),
                                Value = value(item),
                                Selected = isSelected(item)
                              }));
      }
      return returnItems;
    }

    if (items == null)
      return new List<SelectListItem>();

    return items.Select(item => new SelectListItem
                    {
                      Text = name(item),
                      Value = value(item),
                      Selected = isSelected(item)
                    });
  }

  public static IEnumerable<SelectListItem> ToMultiSelectListItems<T>(this IEnumerable<T> items, Func<T, string> name, Func<T, string> value, IEnumerable<int> selectedValues)
  {
    if (selectedValues == null)
      selectedValues = new List<int>();
    return items.ToMultiSelectListItems(name, value, selectedValues.Select(x => x.ToString()));
  }

  public static IEnumerable<SelectListItem> ToMultiSelectListItems<T>(this IEnumerable<T> items, Func<T, string> name, Func<T, string> value, IEnumerable<long> selectedValues)
  {
    if (selectedValues == null)
      selectedValues = new List<long>();
    return items.ToMultiSelectListItems(name, value, selectedValues.Select(x => x.ToString()));
  }

  public static IEnumerable<SelectListItem> ToMultiSelectListItems<T>(this IEnumerable<T> items, Func<T, string> name, Func<T, string> value, IEnumerable<double> selectedValues)
  {
    if (selectedValues == null)
      selectedValues = new List<double>();
    return items.ToMultiSelectListItems(name, value, selectedValues.Select(x => x.ToString()));
  }

  public static IEnumerable<SelectListItem> ToMultiSelectListItems<T>(this IEnumerable<T> items, Func<T, string> name, Func<T, string> value, IEnumerable<decimal> selectedValues)
  {
    if (selectedValues == null)
      selectedValues = new List<decimal>();
    return items.ToMultiSelectListItems(name, value, selectedValues.Select(x => x.ToString()));
  }

  public static IEnumerable<SelectListItem> ToMultiSelectListItems<T>(this IEnumerable<T> items, Func<T, string> name, Func<T, string> value, IEnumerable<string> selectedValues)
  {
    if (items == null)
      return new List<SelectListItem>();

    if (selectedValues == null)
      selectedValues = new List<string>();

    return items.ToMultiSelectListItems(name, value, x => selectedValues.Contains(value(x)));
  }

  public static IEnumerable<SelectListItem> ToMultiSelectListItems<T>(this IEnumerable<T> items, Func<T, string> name, Func<T, string> value, Func<T, bool> isSelected)
  {
    if (items == null)
      return new List<SelectListItem>();

    return items.Select(item => new SelectListItem
                    {
                      Text = name(item),
                      Value = value(item),
                      Selected = isSelected(item)
                    });
  }
}