PHP Undefined Array key and uncaught Type error

Question

My errors are : 

Warning: Undefined array key "email" in C:\xampp\htdocs\loginsystem\db\login.php on line 4

Warning: Undefined array key "password" in C:\xampp\htdocs\loginsystem\db\login.php on line 5

Fatal error: Uncaught TypeError: Unsupported operand types: string + string in C:\xampp\htdocs\loginsystem\db\login.php:9 Stack trace: #0 {main} thrown in C:\xampp\htdocs\loginsystem\db\login.php on line 9

And the lines are:

3. if(isset($_POST['loginsubmit'])){

4.      $email = $_POST['email'];

5.     $password = $_POST['password'];

6.

7. if($email==''){

8.        $msg = "email is required";

9.          header('Location:../login.php?errmsg='+$msg);

      }