Getting a Attempt to invoke virtual method 'android.support.v4.app.FragmentManager android.support.v4.app.FragmentActivity.getSupportFragmentManager()' on a null object reference

Hi
I am trying to close the fragment and go back to my Activity when the user is logged in. So I did:

```
private void initSocialNetwork(SocialNetwork socialNetwork){
getActivity().getSupportFragmentManager().beginTransaction().remove(this).commit();
}

```

The thing is if the user is previosly connect it works like a charm, but if he loggs in it shows this error:
`java.lang.NullPointerException: Attempt to invoke virtual method 'android.support.v4.app.FragmentManager android.support.v4.app.FragmentActivity.getSupportFragmentManager()' on a null object reference`