请教个问题：Expression.getVariableNames方法

现在我自定义了一个函数: get函数。
在Aviator中这样使用，get(today_sum, -1)，getVariableNames方法能返回today_sum， -1这个值能有办法返回吗？

The issue names Expression.getVariableNames and the get(today_sum, -1) call but does not identify a file or requested code change. Start at that method and trace how variable references and literal arguments are represented; done means establishing whether -1 is intentionally excluded or defining the needed behavior and tests.

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