I keep getting this error message and I am unsure what is causing it:

Warning: mysqli_num_rows() expects parameter 1 to be mysqli_result, null given in C:\Program Files\xampp\htdocs\results.php on line 88

Page 88 is referring to the number of rows.
The code is below

<?php
        
// Check that the form has been submitted
if ($_POST) {
    
    //Store the form data in variables
    $form_library_id = $_POST['library_id'];
    $form_earliest_date = $_POST['earliest_date'];
    $form_latest_date = $_POST['latest_date'];
        
    if (array_key_exists('etype', $_POST)) {
        $form_exhibit_type = $_POST['etype'];
    }
    else {
        $form_exhibit_type = "";
        }
        
    //Trim any trailing and leadin spaces from the form data
    $form_library_id = trim($form_library_id);
    $form_exhibit_type = trim($form_exhibit_type);
    $form_earliest_date = trim($form_earliest_date);
    $form_latest_date = trim($form_latest_date);
        
    //Convert earliest and latest dates to integers
    $form_earliest_date = intval($form_earliest_date);
    $form_latest_date = intval($form_latest_date);
        
    //Open a connect to the database
    $link = mysqli_connect('localhost', 'student', 'mmst12009', 'assignment3');
        
    //Define a query
    $query = "
    SELECT
    libraries.library_name,
    exhibits.exhibit_date,
    exhibits.exhibit_type,
    exhibits.exhibit_description,
    exhibits.exhibit_id
    FROM libraries, exhibits
    WHERE libraries.library_id = exhibits.library_id";
        
        
    //Restrict the SQL query with an AND clause if the library ID is not 'any'
    if ($form_library_id != 'any') {
        $query .= " AND libraries.library_id = $form_library_id";
    }
                
    //Restrict the SQL query with an AND clause if the library ID is not 'any'
    if ($form_exhibit_type != "") {
        $query .= " AND exhibits.exhibit_type = '$form_exhibit_type'";
    }
                
    //Restrict the SQL query with an AND clause if the library ID is not 'any'
    if ($form_earliest_date != 0) {
        $query .= " AND exhibits.exhibit_date >= $form_earliest_date";
    }
        
    //Restrict the SQL query with an AND clause if the library ID is not 'any'
    if ($form_latest_date != 0) {
        $query .= " AND exhibits.exhibit_date <= $form_latest_date";
    }
        
    //Restrict the SQL query with an AND clause if the library ID is not 'any'
    if (exhibits.exhibit_id) {
        $query .= " ORDER BY exhibits.exhibit_id";
    }
        
    //Run the query and store the link
    $result = mysqli_query($link, $query);
    
    //Get the number of rows in the result set
    $number_of_rows = mysqli_num_rows($results);
        
    //Close the connection to the database
    mysqli_close($link);
    
    //Exit from the script if no records have been retrieved
    if ($number_of_rows == 0) {
    echo <<<END
    <p>There are no matching records in the database or entered dates might be invalid.<br />
    Use the BACK button on your Web Browser to return to the previous page and try again. </p>
END;
    }
    else {
        
        //Display the table headings
        echo <<<END
        <p>Search results are presented below</p>
        <table border="0" width="900" cellpadding="5" cellspacing="5">
            <tr>
                <th>ID Number</th>
                <th>Library</th>
                <th>Date</th>
                <th>Type</th>
                <th>Description</th>
            </tr>
END;

        //Assign each record in the result to an array
        While ($row = mysqli_fetch_array($result)) {
            //Assign each array element to a variable
            $exhibit_id = $row['exhibit_id'];
            $library_name = $row['library_name'];
            $exhibit_date = $row['exhibit_date'];
            $exhibit_type = $row['exhibit_type'];
            $exhibit_description = $row['exhibit_description'];
            
            
            //Display a table row to each record
            echo <<<END
            <tr>
                <td>$exhibit_id</td>
                <td>$library_name</td>
                <td>$exhibit_date</td>
                <td>$exhibit_type</td>
                <td>$exhibit_description</td>
            </tr>
END;
        }
echo "</table>";
    }
}
?>
    
</body>
</html>

$number_of_rows = mysqli_num_rows($results);

this has to be

 $number_of_rows = mysqli_num_rows($result);

. Best regards...


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