Car dealer LUA problem

Hello everyone! I have this problem LUA. How can I fix it? Many thanks in advance!

[ERROR] addons/williamscardealer/lua/wcd/client/wcd_admin.lua:84: bad argument #1 to ‘SetText’ (string expected, got nil)

  1. SetText - [C]:-1
  2. Rebuild - addons/williamscardealer/lua/wcd/client/wcd_admin.lua:84
    3. OnEnd - addons/williamscardealer/lua/wcd/client/wcd_admin.lua:42
    4. unknown - lua/includes/extensions/client/panel/animation.lua:48

You solve it by contacting the author of the addon, given its a paid one.