code: public void setString(String value) {
      if (this.token == Token.STRING || this.token == Token.NAME) {
        throw new IllegalStateException(
            "String node not created with Node.newString");
      } else {
        throw new UnsupportedOperationException(this + " is not a string node");
      }
    }
docs: Can only be called for a Token.STRING or Token.NAME.
  
  @param value the value to set.