Neb. Rev. Stat. § 21-1993

(a) An officer may resign at any time by delivering notice to the corporation. A resignation is effective when the notice is effective unless the notice specifies a future effective date. If a resignation is made effective at a future date and the corporation accepts the future effective date, its board of directors may fill the pending vacancy before the effective date if the board provides that the successor does not take office until the effective date. (b) A board may remove any officer at any time with or without cause.