接线员？ ：惊讶，惊讶

Question

想象一下情况

int? customerId = null; // works fine
int? customerId = 5; // also fine
int? customerId = someCondition ? 5 : null; // There is no implicit conversion between int and null
int? customerId = someCondition ? 5 : (int?)null; // now is ok

这怎么可能？这是语言规范吗？对我来说，显而易见的是隐式转换。你觉得怎么样？