Check for null activity before getting dashboard categories.

package com.android.settings.dashboard;

import android.app.Activity;

import android.content.Context;

import android.os.AsyncTask;

import android.os.Bundle;

        @Override

        protected void onPostExecute(List<Tile> tiles) {

            final Activity activity = getActivity();

            if (activity == null) {

                return;

            }

            List<DashboardCategory> categories =

                    ((SettingsActivity) getActivity()).getDashboardCategories();

                    ((SettingsActivity) activity).getDashboardCategories();

            mAdapter.setCategoriesAndSuggestions(categories, tiles);

        }

    }