Prevent NullPointerException in getStringValue if no value is set

     * @return Cached value of the characteristic

     */

    public String getStringValue(int offset) {

        if (offset > mValue.length) return null;

        if (mValue == null || offset > mValue.length) return null;

        byte[] strBytes = new byte[mValue.length - offset];

        for (int i=0; i != (mValue.length-offset); ++i) strBytes[i] = mValue[offset+i];

        return new String(strBytes);