code: protected final int getLineNumber(final String lineNumber) {
          if (StringUtils.isNotBlank(lineNumber)) {
              try {
                  return Integer.parseInt(lineNumber);
              }
              catch (NumberFormatException exception) {
                  // ignore and return 0
              }
          }
          return 0;
      }
docs: Converts a string line number to an integer value. If the string is not a
  valid line number, then 0 is returned which indicates a warning at the
  top of the file.
  
  @param lineNumber
  the line number (as a string)
  @return the line number