code: public static String substring(final Object target, final int beginIndex) {
  
          if (target == null) {
              return null;
          }
          final String str = target.toString();
          final int len = str.length();
          Validate.isTrue(beginIndex >= 0 && beginIndex < len, "beginIndex must be >= 0 and < " + len);
  
          // Note this might not free the original string's char[] if using Java < Java7u6
          return str.substring(beginIndex);
      }
docs: <p>
  copy a part of target start beginIndex to the end of target.
  If non-String object, toString() will be called.
  </p>
  
  @param target source of the copy.
  @param beginIndex index where the copy start.
  @return part of target, or {@code null} if target is null.
  @since 1.1.2