Question mark gets appended to URL when error encountered? - php

Question

I have a form. When I submit and try to insert a duplicate record in the database, the page reloads and the error message is logged in the console. However, after* the page reloads, a question mark is already appended to the end of the URL. Why is that so?
Like from this:
http://localhost/project/home
to this (after database error occurred due to duplicate record):
http://localhost/project/home?
Controller:
public function loadBoardManagement()
{
$role = $this->session->userdata('role');
$user_id = $this->session->userdata('user_id');
$board_id = $this->uri->segment(3);
$role = 'Admin';
$user_id = 1;
if ($this->uri->segment(3) == null)
{
$board_id = 178;
}
if ($this->session->userdata('first_board_id') !== null && $board_id == 0)
{
$board_id = $this->session->userdata('first_board_id');
}
$data['boards'] = $this->Board_model->getBoards($role, $user_id);
$data['board_assignees'] = $this->Team_model->getBoardAssignees($board_id);
$data['all_teams'] = $this->Team_model->getAllTeams();
$data['team_quantity'] = $this->Team_model->getBoardTeamsQuantity($board_id);
$data['board_name'] = $this->Board_model->getBoardName($board_id);
$data['board_id'] = $board_id;
$this->load->view('board_management', $data);
}
public function fast_signup()
{
$username = $this->input->post('username');
$password = $this->input->post('password');
$first_name = $this->input->post('first_name');
$last_name = $this->input->post('last_name');
$email = $this->input->post('email');
$role = $this->input->post('role');
$fast_signup = $this->User_model->fastSignup($username, $password, $first_name, $last_name, $email, $role);
if ($fast_signup)
{
echo 'success';
}
else
{
echo $fast_signup;
}
}
javascript:
function addMember()
{
var username = $('#username').val();
var password = $('#password').val();
var first_name = $('#first_name').val();
var last_name = $('#last_name').val();
var email = $('#email').val();
var role = $('#role option:selected').val();
console.log('Role: ' + role);
console.log(username + password + first_name + last_name + email);
$.ajax({
type: 'POST',
url: base_url + 'user/fast_signup', //controller for inserting new members, but the current page is localhost/project/board/loadBoardManagement
data: {
'username': username,
'password': password,
'first_name':first_name,
'last_name': last_name,
'email': email,
'role' : role
},
success: function(msg)
{
if (msg == 'success')
{
console.log('Member created');
window.location.href = window.location.href;
}
else
{
console.log('Failed to create member!' + msg);
}
},
error: function(jqXHR, textStatus, errorThrown)
{
console.log('Response: ' + jqXHR.responseText);
console.log('Status code: ' + textStatus);
console.log('Error thrown: ' + errorThrown);
}
});
}
$('#create_user_member').click(function() {
addMember();
});