fix(lsp): fix lookup of boolean values in workspace/configuration (#18026)

runtime/lua/vim/lsp/util.lua

@@ -1950,8 +1950,8 @@ end
 function M.lookup_section(settings, section)
   for part in vim.gsplit(section, '.', true) do
     settings = settings[part]
-    if not settings then
-      return
+    if settings == nil then
+      return vim.NIL
     end
   end
   return settings