After following, you can keep track of his dynamic information in a timely manner
Courses in the relevant section：PHP data type NULL type
empty只要傳回的值為null或者是false，則返回ture,反之為false。issue（可傳多值，用逗號(hào)隔開）只要傳回的值不是null，則返回false，反之返回ture
2018-06-090個(gè)贊
