Force void
A rare and almost unheard-of anomaly was the void, also known as a blank. It described a living being that seemed to lack any presence in The Force. These individuals could completely mask their appearance and aura, making it impossible for those who encountered them to remember their features.
Nathema became a void after Vitiate's ritual.
The Sith Emperor's use of a ritual stands as one of the earliest documented instances of this occurrence. He employed it to absorb life force, sustaining his immortality. This was seen from his planet, Nathema, and later attempted on a galactic scale. When the Emperor consumed life, he generated a "void" in the Force, draining color and nearly all sound from the surrounding environment.
In 27 BBY, Obi-Wan Kenobi described Granta Omega, the offspring of the Dark Jedi Xanatos, as a "void" in the Force. Kenobi could only speculate that Omega was employing some sort of self-concealment method. Notably, Omega's ability allowed him to evade detection by the Jedi and made him remarkably difficult to remember. Even if someone faintly recalled him, they couldn't provide an accurate description of his appearance.
Another case of this phenomenon emerged in 0 ABY, involving the Human clone assassin X-7. Jedi Knight Ferus Olin observed that X-7 possessed a hollow body, with the Force flowing around him instead of through him. This marked the first and only known instance of such a phenomenon occurring artificially.
The assassin siblings Nyss and Syll Nenn, who were Umbaran, represent perhaps the most remarkable examples. Both siblings demonstrated the ability to create a dark void in the Force, rendering them undetectable to Force sense. Furthermore, the Nenn twins could block Force-sensitives from accessing the Force (although Jaden Korr and his clones were inexplicably powerful enough to overcome this). Their power was so strong that they could neutralize the Force energy within some lightsaber crystals, causing them to shut down completely. Following Syll's death, Nyss Nenn perceived an increase in his ability, despite having always believed that his sister amplified his powers while she was alive.
It is important not to confuse the Force void phenomenon with the Force power known as Force cloak. The former was an inherent ability found among beings naturally inclined toward the dark side of the Force. The latter was a talent or acquired skill primarily used by practitioners of the light side. Both were exceedingly rare.