Call to a member function getPassword() on null in Majora\Component\OAuth\Entity\Token

The prototype of the constructor set the variable `$account` to null by default.

But in the code, it calls the method `getPassword` of the account with no verification of the existence of `$account`.

So when we give `$account = null`, we have an error : 

```
PHP Fatal error:  Call to a member function getPassword() on null in /src/Majora/Component/OAuth/Entity/Token.php on line 61
```
