code: public static long toLong(@Nullable final String longStr) {
          if (!isValidLong(longStr)) {
              throw new IllegalArgumentException(longStr + ExceptionValues.EXCEPTION_DELIMITER + ExceptionValues.INVALID_LONG_VALUE);
          }
          final String stripedLong = StringUtils.strip(longStr);
          return NumberUtils.createLong(stripedLong);
      }
docs: Given a long integer string if it's a valid long (see isValidLong) it converts it into a long integer otherwise it throws an exception
  
  @param longStr the long integer to convert
  @return the long integer value of the longStr
  @throws IllegalArgumentException if the passed long integer string is not a valid long value