Make RecentCallsListActivity#formatPhoneNumber() ignore null or empty phone number.

     * <p>

     * Because of the shared {@link #sEditable} builder, <b>this method is not

     * thread safe</b>, and should only be called from the GUI thread.

     * <p>

     * If the given String object is null or empty, return an empty String.

     */

    private String formatPhoneNumber(String number) {

        if (!TextUtils.isEmpty(number)) {

            return "";

        }

        // Cache formatting type if not already present

        if (sFormattingType == FORMATTING_TYPE_INVALID) {

            sFormattingType = PhoneNumberUtils.getFormatTypeForLocale(Locale.getDefault());