Невозможно неявно преобразовать тип System.Collections.Generi c .IEnumerable <xxx>в System.Collections.Generi c .List <xxx>

Question

Я пытаюсь отсортировать по идентификатору sortorder.

DocumentAttachmentTypesInformation jointOwnershipTypesInformation = (DocumentAttachmentTypesInformation)jointOwnershipTypesInformation.DocumentAttachmentTypes.OrderBy(x=>x.SortOrder);

public class DocumentAttachmentTypesInformation: PartialResult
{
    public List<DocumentAttachmentTypes> DocumentAttachmentTypes { get; set; }
}

public class DocumentAttachmentTypes
{
    public string DocTypeCode { get; set; }
    public string DisplayName { get; set; }
    public string DocumentStore { get; set; }
    public string FileAccept { get; set; }
    public int SortOrder { get; set; }
}