The Kerr-Newman solution to the Einstein field equations has a flat region spanning the ring singularity in the solution; which, unlike the Kerr solution, is not a disk. The nature of this region and its relation to the singularity are the subjects of this paper
http://www.gemarsh.com/wp-content/uploads/FLAT-REGIONS-NEAR-THE-KERR-NEWMAN-SINGULARITY-Rev1.pdf
FLAT REGIONS NEAR THE KERR-NEWMAN SINGULARITY