mysql - Warning: mysqli_fetch_array() expects parameter 1 to be mysqli_result, boolean

Attempting to create a 'Change Password' page for my website, I keep being confronted with these two errors and I can't seem to understand why they are appearing;

Warning: mysqli_fetch_array() expects parameter 1 to be mysqli_result, boolean given in /home/ll12rth/public_html/COMM2735/database/password.php on line 51
Warning: mysqli_free_result() expects parameter 1 to be mysqli_result, boolean given in /home/ll12rth/public_html/COMM2735/database/password.php on line 139

session_start();
$db_hostname = 'localhost';


    $db_database = "****"; //replace with your db name
    $db_username = "****"; //replace with the db username that you created
    $db_password = "****"; //replace with the db password that you created
    $db_status   = 'not initialised';   
    $db_server   = mysqli_connect($db_hostname, $db_username, $db_password);
    $db_status   = "connected";

    if (!$db_server) {
        die("Unable to connect to MySQL: " . mysqli_connect_error());
        $db_status = "not connected";

    } else 

require_once('checklog.php');
require_once("functions.php");



// Grab the form data

$username = trim($_POST['username']);

$password = trim($_POST['password']);
$newpassword = trim($_POST['newpassword']);
$repeatpassword = trim($_POST['repeatpassword']);

if (isset($_POST['submit'])) {
    if ($username && $password) {
        $username = clean_string($db_server, $username);
        $password = clean_string($db_server, $password);
        $query = "SELECT * FROM users WHERE username='$username'";


        $result = mysqli_query($db_server, $query);

        if ($row = mysqli_fetch_array($result)) {
            $db_username = $row['username'];
            $db_password = $row['password'];

            if ($username == $db_username && salt($password) == $db_password) {
                $_SESSION['username'] = $username;
                $_SESSION['logged'] = "logged";


                // header('Location: home.php');
                // PASSWORD CHANGING IS DONE HERE
                if ($newpassword == $repeatpassword) {
                    //From register
                    if (strlen($newpassword) > 25 || strlen($newpassword) < 6) {
                        $message = "Password must be 6-25 characters long";
                    } else {
                        //part 8
                        // Process details here


                        //include file to do db connect

                        if ($db_server) {
                            //clean the input now that we have a db connection

                            $newpassword    = clean_string($db_server, $newpassword);
                            $repeatpassword = clean_string($db_server, $repeatpassword);
                            mysqli_select_db($db_server, $db_database);

                            // check whether username exists


                            $query = "SELECT password FROM users WHERE password='$newpassword'";

                           $result=mysqli_query($db_server, $query);

                            if ($row = mysqli_fetch_array($result)){
                                $message = "This is your current password. Please try again.";
                            } else {
                                //part 9
                                // Process further here

                                $newpassword = salt($newpassword);

                                $query = "INSERT INTO users (password) VALUES 

                                        ('$password')";

                                mysqli_query($db_server, $query) or die("Insert failed. " . mysqli_error($db_server));
                                $message = "
Your password has been changed!
";
                            }


                            mysqli_free_result($result);

                        } else {

                            $message = "Error: could not connect to the database.";

                        }

                        require_once("php/db_close.php"); //include file to do db close
                    }

                }
                //This code appears if passwords dont match 
                else {
                    $message = "
Your new passwords do not match! Try again.
";
                }

            } else {
                $message = "
Incorrect password!
";
            }
        } else {

            $message = "
That user does not exist!
" . "Please try again";
        }
        mysqli_free_result($result);

      //Close connection!
mysqli_close($db_server);

    } else {

        $message = "
Please enter a valid username/password
";


    }
}
?>







    
What do you want to change your password to echo $_SESSION['username'];
?>?



Current Username: 

Current Password: 


New Password: 

Repeat New Password: 



 




echo $message
?>