Symfony2 getId non-object error - php

Question

Hy everybody, i've got a problem with my Bundle when I'm trying to obtain the ID of an user.
$user = $userManager->findUserById($tmpID['uid']);
Where $tmpID['uid'] is the ID of the user and when I'm trying to to $user->getId() I obtain an error.
This is the error
FatalErrorException: Error: Call to a member function getId() on a non-object in /Applications/MAMP/htdocs/Api/src/Api/ApiBundle/Controller/DefaultController.php line 263
MyBundle\Entity\User.php
<?php
namespace MyBundle\Entity;
use Doctrine\ORM\Mapping as ORM;
use FOS\UserBundle\Entity\User as BaseUser;
/**
* #ORM\Entity
* #ORM\Table(name="user")
*/
class User extends BaseUser
{
/**
* #ORM\Id
* #ORM\Column(type="integer")
* #ORM\GeneratedValue(strategy="AUTO")
*
*/
protected $id;
/**
* #var string
*
* #ORM\Column(name="description", type="text", nullable=true)
*/
protected $description;
/**
* #var integer
*
* #ORM\Column(name="genre", type="integer", nullable=false)
*/
protected $genre;
/**
* #var string
*
* #ORM\Column(name="device", type="string", nullable=true)
*/
protected $device;
/**
* #var string
*
* #ORM\Column(name="avatar", type="string", nullable=true)
*/
protected $avatar;
/**
* #var string
*
* #ORM\Column(name="phone", type="integer", nullable=true)
*/
protected $phone;
public function __construct()
{
parent::__construct();
// your own logic
}
public function getDescription() {
return $this->description;
}
public function setDescription($description) {
$this->description = $description;
}
public function getGenre() {
return $this->genre;
}
public function setGenre($genre) {
$this->genre = $genre;
}
public function getDevice() {
return $this->device;
}
public function setDevice($device) {
$this->device = $device;
}
public function getPhone() {
return $this->phone;
}
public function setPhone($phone) {
$this->phone = $phone;
}
public function getAvatar() {
return $this->avatar;
}
public function setAvatar($avatar) {
$this->avatar = $avatar;
}
}

Answer 1

While i was going to the office I get the solution! :)
On my function $tmpIDis an variable wich has the token of an user when that used login into Symfony. The problem it was I was using a token of an user wich didn't exist into the DDBB (Yes, i erased the user 5 minutes before to get that error)
Then, i was trying to obtain a non-existent user and that's the reason why i get NULL for $user
I hope my problem can help other people.
p.s. Thanks to #Javad and #George for the suggestions