PHP: Using is_null() with !$var or isset($var)

Question

While I believe the answer is yes, I have seen the following in legacy code so much, I'm doubting myself. I'm asking for a sanity check from the community.

Legacy Code

if (is_null($result) || !$result) {

Refactored Code

if (!$result) {

Note: I am aware this will throw a Notice if $result is not set.

Question

Is this code logically equivalent?

Code Tests

I tested with all the combinations of PHP false values without receiving Not equal for ....

$false_values = array(false, 0, 0.0, '0', '', null, array(), new stdClass());

foreach ($false_values as $var) {
    if (!$var != (is_null($var) || !$var)) {
        echo 'Not equal for: ';
        var_dump($var);
    }
}

Output

$ php check.php
$

Answer 1

A null variable will evaluate to false in a boolean context. So the statements are logically equivalent - when the variable is null it will be caught by the !$result statement.

Use empty() to prevent a notice-level warning:

if (!empty($result)) {
   // do something
}

Answer 2

Yes, both snippets are equivalent. is_null is defined as:

Returns TRUE if var is null, FALSE otherwise.

The documentation also makes it clear that is_null throws out a warning when the variable is undefined, as does a simple boolean evaluation of $result. If $result is unset, is_null($result) is true and you therefore get one warning - the same behavior as you'd with !$result.

Since the boolean evaluation of NULL is (unsurprisingly) false, we can simply test out all interesting values:

$result  is_null($result)  !$result   is_null($result) || !$result
(unset)   true(+warn)     true(+warn)          true (+warn)
null         true            true              true
false(-y)    false           true              true
true(-ish)   false           false             false

Note that the results of is_null and !$result are identical for all values that evaluate to false as well for all ones evaluating to true. Therefore, no further distinction (say, by testing 0, "", etc.) is necessary.