code: public AstNode handleUnknownToken( DdlTokenStream tokens,
                                         String tokenValue ) throws ParsingException {
          assert tokens != null;
          assert tokenValue != null;
          // DEFAULT IMPLEMENTATION DOES NOTHING
          return null;
      }
docs: Utility method subclasses can override to check unknown tokens and perform additional node manipulation. Example would be
  in Oracle dialect for CREATE FUNCTION statements that can end with an '/' character because statement can contain multiple
  statements.
  
  @param tokens the {@link DdlTokenStream} representing the tokenized DDL content; may not be null
  @param tokenValue the string value of the unknown token; never null
  @return the new node
  @throws ParsingException