if statement evaluates to true on NULL variable when using is_null()

Question

So I've got a form with a modal, that modal has 3 rows with 2 text fields each, if the user (me in this prod case) fills out only 2 rows, and leave the other row empty, that 3rd value should be NULL.

In my script I've got:

if (!is_null($_POST['packageDependencies']['bundle'][2])) {
$packageDependency3 = $_POST['packageDependencies']['bundle'][2] . "|" . $_POST['packageDependencies']['version'][2] . "|" . $_POST['packageDependencies']['repository'][2];
$depends = "<key>dependencies</key>
            <array>
                <string>$packageDependency1</string>
                <string>$packageDependency2</string>
                <string>$packageDependency3</string>
            </array>
            ";

}

So I'm checking if (!is_null($3rdRow)) { //Do this }, but the variable $_POST['packageDependencies']['bundle'][2] is in fact NULL, as I use var_dump($_POST['packageDependencies']['bundle'][2]); and I get NULL printed to the page, but the if statement is still processing as if it isn't NULL.

$depends gets fwrite() to an XML file, and when I open it, I only see || and but that shouldn't be there as the variable is NULL as I entered no values into those input fields.

If you are just checking to see if there isn't user input then try empty() — gview
– gview, Commented May 18, 2018 at 17:22
@WillardSolutions !empty() seems to do the trick, but what's up with !is_null() not working? — Brian
– Brian, Commented May 18, 2018 at 17:25
There are some great answers here that will settle your query — Mm-Art-In
– Mm-Art-In, Commented May 18, 2018 at 17:26
@Martin Thanks for the info, I've decided to use == operands to be less ambiguous as one of those posts states, and I'll get in the practice of doing that instead of using is_null() and empty() from now on. — Brian
– Brian, Commented May 18, 2018 at 17:30

gview · Accepted Answer · 2018-05-18 17:31:15Z

1

Given my advice, a more complete solution would be:

if (!empty(trim($_POST['packageDependencies']['bundle'][2]))) {

NULL is a specific state of a variable that involves the way PHP associates the name of a variable with a variable location. You can think of it like a flag, that indicates a variable name exists, but there is no storage location associated with it. There are a number of situations that empty with trim will catch that will bypass a check against null.

answered May 18, 2018 at 17:31

gview

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1 Comment

Brian Over a year ago

This makes sense, as trim() removes whitespaces, and if a user accidentally hits the space key within one of the fields but doesn't notice, it won't cause issues. I'll add the trim() function in, thank you so much! I learn something new everyday!

Brian · Accepted Answer · 2018-05-18 17:37:22Z

0

Even though !empty() did the trick, I've decided to use == to be less ambiguous. The answers found here are quite intuitive.

EDIT: As per @gview, adding (!empty(trim($var))) is the best bet as if a user accidentally presses the space key after a tab, it will avoid any errors.

edited May 18, 2018 at 17:37

answered May 18, 2018 at 17:29

Brian

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