PHP 中的 ==null;is_null();empty()

empty():   0, null, ''


==null :    '', null
 ==null: 0, null, ''
//change to:
function is_emptystring_or_null($str) {
     return (is_null($str) || ($str === ''));
}

is_null():  ===null

         isset  is_null ===null  ==null  empty
 null |   F   |   T   |   T   |   T   |   T   |
 true |   T   |   F   |   F   |   F   |   F   |
false |   T   |   F   |   F   |   T   |   T   |
    0 |   T   |   F   |   F   |   T   |   T   |
    1 |   T   |   F   |   F   |   F   |   F   |
   \0 |   T   |   F   |   F   |   F   |   F   |
unset |   F   |   T   |   T   |   T   |   T   |
  ""  |   T   |   F   |   F   |   T   |   T   |
  []  |   T   |   F   |   F   |   T   |   T   |