TelephonyManager.getNetworkCountryIso() getting null in ANDROID 6.0

Country name is getting null using TelephonyManager in android 6.0 version.Below 6.0 country name is getting and i also gave permissions but its not working.Could you please help me.

private static final String[] PERMISSIONS = {
        Manifest.permission.READ_PHONE_STATE,
        Manifest.permission.ACCESS_COARSE_LOCATION
};
private TelephonyManager mTelephonyManager;
private EditText et_ind,et_us;
private Button bt_money_convert;

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);       
    checkPermissions();
}
private void checkPermissions() {
    // Checks the Android version of the device.
    //if ((Build.VERSION.SDK_INT >= Build.VERSION_CODES.M) ||(Build.VERSION.SDK_INT >= Build.VERSION_CODES.N)) {
    if (Build.VERSION.SDK_INT >= 23){
        TelephonyManager mTelephonyManager= (TelephonyManager) this.getSystemService(Context.TELEPHONY_SERVICE);
        String getCountryName1 =mTelephonyManager.getNetworkCountryIso();
        Toast.makeText(MainActivity.this,"Location--->"+getCountryName1,Toast.LENGTH_LONG).show();

    } else {
        TelephonyManager mTelephonyManager= (TelephonyManager) this.getSystemService(Context.TELEPHONY_SERVICE);
        String getCountryName =mTelephonyManager.getNetworkCountryIso();
        Toast.makeText(MainActivity.this,"Location--->"+getCountryName,Toast.LENGTH_LONG).show();

    }
}