Is an employee entitled to a vested contractual right to a pension?

of pensions is a necessary one since pension systems must be kept flexible to permit adjustments in accord with changing conditions and at the same time maintain the integrity of the system and carry out its beneficent policy.... [] Thus it appears ... that an employee may acquire a vested contractual right to a pension but that this right is not rigidly fixed by the specific terms of the legislation in effect during any particular period in which he serves. The statutory language is subject to the implied qualification that the governing body may make modifications and changes in the system. The employee does not have a right to any fixed or definite benefits, but only to a substantial or reasonable pension. There is no inconsistency therefore in holding that he has a vested right to a pension but that the amount, terms and conditions of the benefits may be altered.¹⁸ (Kern v. City of Long Beach, supra, 29 Cal.2d 848, 854855, 179 P.2d 799.)