What are the differences between using != NULL and is_null() to check for null values in PHP variables?

When checking for null values in PHP variables, using != NULL compares the value of the variable against NULL, while is_null() specifically checks if the variable is NULL. Using != NULL may not work as expected if the variable contains a value like 0, empty string, or false, as these are considered falsy values in PHP. On the other hand, is_null() will only return true if the variable is explicitly set to NULL.

// Using != NULL to check for null values
if ($variable != NULL) {
    // Variable is not null
} else {
    // Variable is null
}

// Using is_null() to check for null values
if (is_null($variable)) {
    // Variable is null
} else {
    // Variable is not null
}