There is no option to ask a mage to join the kingdom

This issue is about asking a mage to join the kingdom. In a conversation with other person, ruler can ask the person that he speak with to join his kingdom. In the other hand, notice that when ruler speak to mage there is no option to ask a mage to join the kingdom. Since one of the feature in the game user can use Toggle Mage Control by press M. You can see it here.