Why are the results of php, is_null and ==null different?

is_null() function detects whether a variable is NULL
null is a special data type in PHP that represents a null value, which means that no value null (null value) is set for the variable
For example:
< ;?php
$str = '';
var_dump(is_null($str));
//returns false. Although the variable $str is assigned a value of empty, it is not of null type, so it returns false
var_dump($str == null);
//Return true, == only determines whether the values ​​are equal, not the type of data, so the empty
value of the variable $str is equal to null (equivalent to empty value)
var_dump($str === null);
//Return false, === not only determines whether the values ​​are equal, but also determines the type of data, so the empty
value of the variable $str (character string) is not equal to null (special data type)
?>

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