jruby null pointer exception

code-snippet.java

  private JRubyInterceptor(String scriptPath, String className) {
    this.scriptPath = scriptPath;
    this.className = className;

    try {
      logger.info("Trying to read ruby script from " + scriptPath);
      Reader reader = new FileReader(scriptPath);
      jruby.eval(new BufferedReader(reader));
      logger.info("Trying to create our interceptor class by evaluating " + className + ".new");
      this.rubyInterceptor = jruby.eval(className + ".new");
    } catch (FileNotFoundException e) {
      throw new IllegalArgumentException("Script file not found: " + scriptPath, e);
    } catch (ScriptException e) {
      throw new IllegalArgumentException("Error executing script: " + scriptPath, e);
    }
  }