两个查询的Linq Union在字符串赋值时抛出null异常

Question

我有这两个查询，其中第一个返回组织与部门，第二个返回没有部门的组织，之后我使用Union()作为我的最终查询，因为我想在表中显示两个结果。

Union()要求在两个查询中完全使用相同的属性，因此我必须在第二个查询中分配“空”Department对象，但我需要将Department Name设为空它引发了我null exception，我不知道它为什么要抛出它，它对我来说没有意义。

当我尝试将organization.Name分配到Department.Name时突然发现它根本没有扔给我null exception。

是否有可能将空字符串分配到Department name？

var query1 = UserAccountOwnSuppliers
                .Where(organization => organization.IsBuyer)
                    .SelectMany(organization => organization.Departments
                        .Select(department =>
                            new UserAccountMarketsForSupplierDTO
                            {
                                Organization = new OrganizationBaseDTO
                                {
                                    Id = organization.Id,
                                    Name = organization.Name,
                                    RegionId = organization.RegionId,
                                    CreatorDepartmentId = organization.CreatorDepartmentId,
                                    CreatorOrganizationId = organization.CreatorOrganizationId,
                                    CreatorId = organization.CreatorId,
                                },
                                Department = new DepartmentBaseDTO
                                {
                                    Id = department.Id,
                                    Name = department.Name
                                }
                            })).OrderBy(dto => dto.Organization.Name);

        var query2 = UserAccountOwnSuppliers
            .Where(organization => organization.IsBuyer)
            .Select(organization => new UserAccountMarketsForSupplierDTO
            {
                Organization = new OrganizationBaseDTO
                {
                    Id = organization.Id,
                    Name = organization.Name,
                    RegionId = organization.RegionId,
                    CreatorDepartmentId = organization.CreatorDepartmentId,
                    CreatorOrganizationId = organization.CreatorOrganizationId,
                    CreatorId = organization.CreatorId,
                },
                Department = new DepartmentBaseDTO
                {
                    Id = 0,
                    //here it throws null exception when I try to assign some value
                    Name = "---"
                }
            }).OrderBy(dto => dto.Organization.Name); ;

        var query = query2.Union(query1);

        return query.OrderBy(dto => dto.Organization.Name);

DTO的

public class DepartmentBaseDTO : IEntity<int>
{
    public string Name { get; set; }
    public int Id { get; set; }
}

public class OrganizationBaseDTO : IEntity<int>
{
    public string Name { get; set; }
    public int? ParentOrganizationId { get; set; }
    public int? RegionId { get; set; }
    public int CreatorId { get; set; }
    public int CreatorOrganizationId { get; set; }
    public int CreatorDepartmentId { get; set; }
    public string Code { get; set; }
}

public class UserAccountMarketsForSupplierDTO : IEntity<int>
{
    public OrganizationBaseDTO Organization { get; set; } = new OrganizationBaseDTO();
    public DepartmentBaseDTO Department { get; set; } = new DepartmentBaseDTO();     
}

栈跟踪 https://pastebin.com/j81yBYYU