to meet their burden under the definiteness requirement. {27} To the extent that Plaintiffs argue that the district court has an affirmative duty to define the class, we respond that it is Plaintiffs who bear the burden to properly define the class or any subclasses; any duty on the court is discretionary. U.S. Parole Comm’n v. Geraghty, 445 U.S. 388, 407-08, 100 S.Ct. 1202, 63 L.Ed.2d 479 (1980); Lundquist v. Sec. Pac. Auto. Fin. Servs. Corp., 993 F.2d 11, 14-15 (2d Cir.1993) (per curiam). We agree, however, that when possible, the district court should consider exercising its discretion to modify a proposed class definition or create subclasses, although it is under no obligation to do so in situations such as this ease where it would be unduly burdensome. Abrams, 719 F.2d at 31 (<HOLDING>); see Thomas, 54 F.R.D. at 249 (holding that a
holding that the mere existence of individualized factual questions with respect to the class representatives claim will not bar class certification holding the court was not required to decide the issue of whether the district court properly certified a rule 23b2 class because the court already concluded that the district court appropriately certified the class under rule 23b3 citing authority for the proposition that a court need only find that a class action may be maintained under any of the three subdivisions holding that the district court is under no duty to devise a manageable class especially where the difficulties with respect to notice and damages are staggering holding that where the board of immigration is permitted to reopen proceedings in exceptional circumstances its decision not to reopen a case is unreviewable because there are no statutory regulatory or caselaw definitions of exceptional circumstances  and  thus no manageable standard to apply on review holding where there is no duty to defend there is no duty to indemnify