(a) In general. (1)(i) Section 402 relates to the taxation of the beneficiary of an employees' trust. If an employer makes a contribution for the benefit of an employee to a trust described in section 401(a) for the taxable year of the employer which ends within or with a taxable year of the trust for which the trust is exempt under section 501(a), the employee is not required to include such contribution in his income except for the year or years in which such contribution is distributed or made available to him. It is immaterial in the case of contributions to an exempt trust whether the employee's rights in the contributions to the trust are forfeitable or nonforfeitable either at the time the contribution is made to the trust or thereafter.