Fix NPE when opening tether preference.

import android.content.Context;

import android.os.SystemProperties;

import android.support.annotation.VisibleForTesting;

import android.telephony.CarrierConfigManager;

public class TetherUtil {

    private static boolean isEntitlementCheckRequired(Context context) {

    @VisibleForTesting

    static boolean isEntitlementCheckRequired(Context context) {

        final CarrierConfigManager configManager = (CarrierConfigManager) context

             .getSystemService(Context.CARRIER_CONFIG_SERVICE);

        if (configManager == null || configManager.getConfig() == null) {

            // return service default

            return true;

        }

        return configManager.getConfig().getBoolean(CarrierConfigManager

             .KEY_REQUIRE_ENTITLEMENT_CHECKS_BOOL);

    }

/*

 * Copyright (C) 2017 The Android Open Source Project

 *

 * Licensed under the Apache License, Version 2.0 (the "License");

 * you may not use this file except in compliance with the License.

 * You may obtain a copy of the License at

 *

 *      http://www.apache.org/licenses/LICENSE-2.0

 *

 * Unless required by applicable law or agreed to in writing, software

 * distributed under the License is distributed on an "AS IS" BASIS,

 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.

 * See the License for the specific language governing permissions and

 * limitations under the License.

 */

package com.android.settingslib;

import android.content.Context;

import org.junit.Before;

import org.junit.Test;

import org.junit.runner.RunWith;

import org.mockito.Mock;

import org.mockito.MockitoAnnotations;

import org.robolectric.annotation.Config;

import static com.google.common.truth.Truth.assertThat;

import static org.mockito.Mockito.when;

@RunWith(SettingLibRobolectricTestRunner.class)

@Config(manifest = TestConfig.MANIFEST_PATH, sdk = TestConfig.SDK_VERSION)

public class TetherUtilTest {

    @Mock

    private Context mContext;

    @Before

    public void setUp() {

        MockitoAnnotations.initMocks(this);

    }

    @Test

    public void isEntitlementCheckRequired_noConfigManager_returnTrue() {

        when(mContext.getSystemService(Context.CARRIER_CONFIG_SERVICE)).thenReturn(null);

        assertThat(TetherUtil.isEntitlementCheckRequired(mContext)).isTrue();

    }

}