NullReferenceException при вызове Select.BuildSqlText

Добрый день, столкнулся с проблемой преобразования sql запроса через Select.BuildSqlText. Вылетает NullReferenceException при попытке выстроить такой запрос:

 

with UpStructure (Id, Name, UsrHoldingId, UsrSPRId, UsrChainId, TypeId) as (
	select Id,
		Name,
		UsrHoldingId, 
		UsrSPRId, 
		UsrChainId,
		TypeId
	from [TerrasoftDB].[dbo].[Account]
	where Id = @srcId
 
	union all
 
	select up.Id,
		up.Name,
		up.UsrHoldingId, 
		up.UsrSPRId, 
		up.UsrChainId,
		up.TypeId
	from [TerrasoftDB].[dbo].[Account] as up
	inner join UpStructure as down 
	on up.Id in (down.UsrHoldingId, down.UsrSPRId, down.UsrChainId)
),
 
FullStructure (Id, Name, UsrHoldingId, UsrSPRId, UsrChainId, TypeId) as (
	select Id,
		Name,
		UsrHoldingId, 
		UsrSPRId, 
		UsrChainId,
		TypeId
	from [TerrasoftDB].[dbo].[Account]
	where Id = (select Id from UpStructure
				where UsrHoldingId is null
				and UsrSPRId is null
				and UsrChainId is null)
 
	union all
 
	select down.Id,
		down.Name,
		down.UsrHoldingId, 
		down.UsrSPRId, 
		down.UsrChainId,
		down.TypeId
	from [TerrasoftDB].[dbo].[Account] as down
	inner join FullStructure as up 
	on up.Id in (down.UsrHoldingId, down.UsrSPRId, down.UsrChainId)
)
 
select * from FullStructure

кусок C# кода:

 

        public async Task<Dictionary<Guid, List<UsrAccountTypeEntityCode>>> GetAccountStructure(Guid guid, string sqlScriptName)
        {
            if (guid == Guid.Empty)
                throw new ArgumentNullException(nameof(guid));
 
            var declareString = "declare @srcId uniqueidentifier \r\n" +
                $"set @srcId = '{guid}';\r\n";
            var sql = System.IO.File.ReadAllText("GetStructure.sql"); //debbug
 
            var sb = new StringBuilder(declareString);
            sb.Append(sql);
 
            var select = new Select(UserConnection);
            select.BuildSqlText(sb);
            ...
        }

NullReferenceException где-то глубоко при вызове this.DBEngine.BuildQuerySqlText(sb, this) в классе Select