try checking if the bundle had been passed or not like this:

Bundle extras = getIntent().getExtras();
if(extras!=null){
    if(extras.containsKey("secondUser")){
        Log.i("test", "yes");
        String[][] cost = (String[][]) extras.getSerializable("secondUser");
    }else{
        Log.i("test", "no");
    }
}

This will not crash your app with NullPointerException and you will also know if the value has been passed to your activity or not in your logcat.

I know that there are already a few posts about this, i tried all of them but nothing worked for me.
As the title says i want to pass a two-dimensional-array to an activity from a fragment, this is my code:

Fragment (passing array):

Intent intent = new Intent(getActivity(), SingleChatActivity.class);
Bundle mBundle = new Bundle();
mBundle.putSerializable("secondUser", requestedFriendships);
intent.putExtras(mBundle);
startActivity(intent);

Activity (receiving array):

Bundle extras = getIntent().getExtras();
String[][] cost = (String[][]) extras.getSerializable("secondUser");

requestedFriendships is here my Array filled with data. As an error i get a NullPointerException.

Does someone have any idea what is wrong or what am i missing? Really grateful for any awnser!