Left join entity is never null

未指定源文件或测试。首先针对 SQLProvider v1.1.93 重现 issue 中的两种查询形式，重点关注 leftOuterJoin、DefaultIfEmpty() 以及报告中的默认值实体。完成标准是记录或测试受支持的语法，以及缺少实体时的预期行为。

Describe the bug
I am trying to left join "sheets" entity but I can't get it to work properly.

The documentation says that leftOuterJoin is not supported, but I see examples on stackoverflow of people saying this works.
For me it does not.

query {
        for e in ctx.Dbo.TimeEntries do
        join t in ctx.Dbo.ProjectTasks on (e.TaskId = t.Id)
        leftOuterJoin sheet in ctx.Dbo.DrawingLogSheets on (e.SheetId = Some sheet.Id) into sheetResults
        for s in sheetResults.DefaultIfEmpty() do
        where (e.Email = Some email && e.Date = dateOnly)
        select (toTimeEntry(e, t, s))
    }

This fails with an error.

I also tried this approach:

query {
        for e in ctx.Dbo.TimeEntries do
        join t in ctx.Dbo.ProjectTasks on (e.TaskId = t.Id)
        join s in (!!) ctx.Dbo.DrawingLogSheets on (e.SheetId = Some s.Id)
        where (e.Email = Some email && e.Date = dateOnly)
        select (toTimeEntry(e, t, s))
    }

This kind of works, but sheet is never null when it is missing; instead, it has all its values defaulted. For example, its ID field is a new guid (all zeros), and its string values are all empty string. I suppose I could check for defaulted guid, but this just feels like something is not right.

To Reproduce

Expected behavior
In the first example (leftOuterJoin), I just want to verify whether this syntax is supposed to be supported or not.
In the second example (!!), I would expect the sheet entity to be null when no sheet is joined, but instead it is instantiated with all default values.

Screenshots

Desktop (please complete the following information):

• Windows
• SQLProvider is v1.1.93

Smartphone (please complete the following information):

• Device: [e.g. iPhone6]
• OS: [e.g. iOS8.1]
• Browser [e.g. stock browser, safari]
• Version [e.g. 22]

Additional context
Add any other context about the problem here.