Message: Trying to access array offset on value of type null

This error means that you are trying to use null as array. What your code trying to do here is like null['char_data'], which obviously makes no sense.

There could be two reasons for this error to appear:

1. Some function may return either a meaningful array or null.
2. A bug in your code.

When null value is expected

There are cases when null is a legitimate value. For example, a function may return either a meaningful array or null, as it happens with PHP mysqli API. In this case this return value has to be tested first, like this:

    $row = $stmt->fetch_assoc();
    if ($row !== null) { // the record was found and can be worked with
        echo $row['name'];
    }

Another case is when you are dealing with outside variable or any other situation when things are not under your control. In this case, you have to validate that input data first.

For example, in case you are expecting an array from a form, and this array is obligatory, validate it and return an error, like

if (!isset($_POST['options']) || !is_array($_POST['options'])) {
   // inform the user and stop execution
} else {
    $options = $_POST['options'];
}
// now you can safely use count() on $options

In case the array is optional, you may initialize it as empty array:

if (!isset($_POST['options'])) {
    $options = [];
} elseif (!is_array($_POST['options'])
   // inform the user ad stop execution
} else {
    $options = $_POST['options'];
}
// now you can safely use count() on $options

In case it's a bug in your code

You have to fix it.

You must understand that using isset() won't fix the problem. It will just sweep it under the rug, effectively acting as the error suppression operator, so when some your function will start returning incorrect value, you will never get a helpful error message that would have explained, why your program suddenly stopped working.

The given warning:

Warning - Trying to access array offset on value of type null - PHP 7.4.0 #7776

results form this snippet $key = $key[1]; and can be solved by using this instead:

$key = isset($key[1]) ? $key[1] : null;

Quick Fix for those that are not looking for the in depth detail, which I appreciated. I was using an outdated setup instructions for XenForo

if ($_POST['t'] == 0) {
    /* get by id */
    $finder = \XF::finder('XF:User');
    $user = $finder->where('user_id', $_POST['v'])->fetchOne();
} else {
    /* get by name */
    $finder = \XF::finder('XF:User');
    $user = $finder->where('username', $_POST['v'])->fetchOne();
}
$columns = array("user_id", "username", "last_username");
for ($i = 0; $i < sizeof($columns); $i++) {
    $column = $columns[$i];
    $columns[$i] = array($column, $user[$column]);
}

so just add the php !isset || !is_array

if (!isset($_POST['t']) || !is_array($_POST['t'])) {
    /* get by id */
    $finder = \XF::finder('XF:User');
    $user = $finder->where('user_id', $_POST['v'])->fetchOne();
} else {
    /* get by name */
    $finder = \XF::finder('XF:User');
    $user = $finder->where('username', $_POST['v'])->fetchOne();
}
$columns = array("user_id", "username", "last_username");
for ($i = 0; $i < sizeof($columns); $i++) {
    $column = $columns[$i];
    $columns[$i] = array($column, $user[$column]);
}

Before accessing any element within the array, ensure the entire array itself is not null you can use if statement and isset() methood check like below

if(!isset($cOTLdata)){
//Handle the case where array is null
  return;
}
$list=$cOTLdata['char_data'];
}

if you are facing this issue in mpdf then

1. go to Mpdf.php
2. search for this line: $e = $this->otl->applyOTL($e, $this->CurrentFont['useOTL']);
3. replace it with :$e = preg_replace("/[\xe2\x80\x8c\xe2\x80\x8d\xe2\x80\x8e\xe2\x80\x8f]/u", '', $e); $e = preg_replace("/[\xef\xbb\xbf]/u", '', $e);

I am new to PHP but this fixed my issue.

  $user_type_res = $connection->query(query: "SELECT `user_type` from `users` WHERE email='$email'");
      $user_type = $user_type_res->fetch_assoc()['user_type'];

So the idea is to query the column on the table first then fetch the association of that column to get the data

<?php
require './connect/config.php'; // Database connection
session_start();

if (!isset($_GET['id']) || empty($_GET['id'])) {
    echo "<h2 class='text-center text-danger'>Category not found!</h2>";
    exit;
}

$category_id = intval($_GET['id']);

// Fetch Category Details
$categoryQuery = $conn->prepare("SELECT * FROM categories WHERE id = ?");
$categoryQuery->bind_param("i", $category_id);
$categoryQuery->execute();
$categoryResult = $categoryQuery->get_result();
$category = $categoryResult->fetch_assoc();

if (!$category) {
    echo "<h2 class='text-center text-danger'>Invalid category!</h2>";
    exit;
}

// Fetch Products under this Category
$productQuery = $conn->prepare("SELECT * FROM products WHERE category_id = ?");
$productQuery->bind_param("i", $category_id);
$productQuery->execute();
$productResult = $productQuery->get_result();
?>