Hernandez v. United States, 778 F.3d 1230 (11th Cir. Mar. 2, 2015) (reversing district court denial of an evidentiary hearing on a motion to vacate sentence under 28 U.S.C. 2255 based on ineffective assistance of counsel, since the motion alleged facts that, if true, would entitle the defendant to relief, but a district court need not hold an evidentiary hearing if the allegations are patently frivolous, based upon unsupported generalizations, or affirmatively contradicted by the record).