At the core of the Jedi's lightsabre training is what the Jedi Masters affectionately call "Form Zero". It was not a true form and therefore never counted among the main seven. In short: it was the act of wielding a lightsaber without the blade. It taught Jedi the symbolic power of a lightsaber and how in many situations its mere presence could prevent a fight; that the threat of violence is sometimes more useful than the actual violence itself.
While in practice it is unheard of for Dark Jedi to even acknowledge Form 0, its message should not be ignored. Even an inactive lightsaber is a powerful tool. It is normal for Journeymen to learn the basics of Form 0 in their initial training with a low-powered lightsaber, called a 'Training Saber' in order to appreciate the power of a real weapon.