Fix bad remove type

Fix 584

Author: CppCXY

crates/emmylua_code_analysis/src/db_index/type/type_ops/mod.rs

@@ -18,8 +18,17 @@ impl TypeOps {
     pub fn apply(&self, db: &DbIndex, source: &LuaType, target: &LuaType) -> LuaType {
         match self {
             TypeOps::Union => union_type::union_type(source.clone(), target.clone()),
-            TypeOps::Remove => remove_type::remove_type(db, source.clone(), target.clone())
-                .unwrap_or(LuaType::Never),
+            TypeOps::Remove => {
+                let result = remove_type::remove_type(db, source.clone(), target.clone());
+                if let Some(result) = result {
+                    return result;
+                }
+
+                match &source {
+                    LuaType::Nil => LuaType::Never,
+                    _ => source.clone(),
+                }
+            }
         }
     }
 }