Unexpected typechecking (with classes only?)

还没有人认领这个 Issue。

### How are you using the lua-language-server?

Visual Studio Code Extension (sumneko.lua)

### Which OS are you using?

MacOS

### What is the issue affecting?

Type Checking

### Expected Behaviour

```lua
---@param a string
---@return string
local function expandHeader(a) return a end

---@class baz
---@field header string?

---@type baz
local foo = {}
local bar = foo.header
expandHeader(foo.header) -- param-type-mismatch
expandHeader(bar) -- param-type-mismatch
```

### Actual Behaviour

```lua
---@param a string
---@return string
local function expandHeader(a) return a end

---@class baz
---@field header string?

---@type baz
local foo = {}
local bar = foo.header
expandHeader(foo.header) -- NO WARNING
expandHeader(bar) -- param-type-mismatch
```

### Reproduction steps

See actual behavior

### Additional Notes

_No response_

### Log File

_No response_

从 issue 中的 Lua 复现开始，检查带注解类的 nullable 字段的类型检查路径。确认 expandHeader(foo.header) 和 expandHeader(bar) 的行为；当两次调用都报告预期的参数类型不匹配时即表示完成。

由索引模型根据 Issue 内容生成。