code: private Node createCatch(String varName, Node catchCond, Node stmts,
                               int lineno) {
          if (catchCond == null) {
              catchCond = new Node(Token.EMPTY);
          }
          return new Node(Token.CATCH, createName(varName),
                          catchCond, stmts, lineno);
      }
docs: Catch clause of try/catch/finally
  @param varName the name of the variable to bind to the exception
  @param catchCond the condition under which to catch the exception.
  May be null if no condition is given.
  @param stmts the statements in the catch clause
  @param lineno the starting line number of the catch clause