Diagnostics nil check is suppressed by the field value matching the parameter type #3056

How are you using the lua-language-server?

Visual Studio Code Extension (sumneko.lua)

Which OS are you using?

Windows

What is the issue affecting?

Diagnostics/Syntax Checking

Expected Behaviour

Diagnostics nil check does not depend on the field parameter value

---@class A
---@field b string

---@type A?
local a

if a.b == "string1" then end  -- Need check nil
if a.b == "string" then end  -- Need check nil

Actual Behaviour

The string value "string" suppresses the triggering of diagnostics, because of type string of field b.

Reproduction steps

1. Copy the sample code
2. Check the diagnostics a.b == "string" when a should trigger "Need check nil"

Additional Notes

No response

Log File

No response