Unexpected typechecking (with classes only?)

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

---@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

---@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

Start with the Lua reproduction in the issue and inspect the type-checking path for nullable fields on annotated classes. Confirm the behavior for both expandHeader(foo.header) and expandHeader(bar); done means both calls report the expected parameter-type mismatch.