Hello guys, I'm getting following error message. Please help me. Thanks

Notice: Trying to get property of non-object in
C:\xampp\htdocs\my\include\user_functions.php on line 34

Here is my Code

$conn = db_connection();
    if($conn == false) {
        user_error('Unable to connect to database');
        return false;
    }
    $query = "UPDATE user SET passwd = '".$new_passwd."'
            WHERE username = '".$username."'  ";

    $result=$conn->query($query);
    if($result == false) {
        user_error('Query Error'.$conn->error);
        return false;
    }           

    if($result->num_rows == 1) {
        echo 'Password changed';
    } else {
            echo 'Failed ';
    }

here is my db_connection

function db_connection() {
    $db = new mysqli('localhost','root','','php_login');
    if(!$db) {
        echo 'Could not connect to database server';
    } else {
        return $db;
    }
}