code: protected Object actuallyEvaluate(String exp, Map<String, ? extends Object> contextMap, LaContainer container, String firstName,
              Object firstComponent) {
          final ScriptEngine engine = prepareScriptEngineManager().getEngineByName("javascript");
          if (firstName != null) {
              engine.put(firstName, firstComponent);
          }
          try {
              return engine.eval(exp);
          } catch (ScriptException | RuntimeException e) {
              throwJavaScriptExpressionException(exp, contextMap, container, e);
              return null; // unreachable
          }
      }
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