PHP form entry 0 returning NULL - php

Question

// removed from original post
// if (!empty($_POST['user_inputA2'])) {
function formA2 () {
function test_input_A2($data) {
$data = trim($data);
$data = stripslashes($data);
$data = htmlspecialchars($data);
return $data;
}
?>
<form id="questionA2" action="<?php echo htmlspecialchars($_SERVER['PHP_SELF']);?>" method="post">
<input type="text" name="user_inputA2" value="<?php if(isset($_POST['user_inputA2'])) { echo htmlentities ($_POST['user_inputA2']); }?>"/><br>
<input type="submit" name="user_inputA2Submit" style="position: absolute; left: -9999px"/>
</form>
<?php
if (!empty($_POST['user_inputA2']) && $_POST['user_inputA2'] !=="0") {
$user_inputA2 = test_input_A2($_POST["user_inputA2"]);
// more variables here, per line -- and add them to the ="" above.
return $user_inputA2;
}
}
UPDATE -- code below is what ended up working
if ($_SERVER["REQUEST_METHOD"] == "POST") {
if ($_POST['user_inputA2'] !="") {
$user_inputA2 = test_input_A2($_POST["user_inputA2"]);
// more variables here, per line -- and add them to the ="" above.
return $user_inputA2;
}
}
}
If I enter anything besides 0, my PHP code for !empty executes. I have tried alternatives of isset, !== NULL, and even an alternative IF statement of (... === "0" || ... === 0) { $user_inputA2 = "0" }. Still returns null and the page responds as if nothing was entered in the form.
How can I get the rest of the code to execute if the form entry is 0 (de facto isset or !empty) ?

Answer 1

You could try this:
<?php
// No need for this line
// if ($_SERVER["REQUEST_METHOD"] == "POST")
if(isset($_POST['user_inputA2']) && $_POST['user_inputA2'] !== '') {
$user_inputA2 = test_input_A2($_POST['user_inputA2']);
return $user_inputA2;
}

Answer 2

I found a fix on the receiving side. The code above does return the string of 0, but for implementation, I was asking if comparisons such as empty, !empty, isset. I changed those to if comparison either == "" or != "", and then the return value of 0 was treated as that actual value, etc.
Sorry the solution ended up being downstream in code from what I posted. Thanks again, everyone.