app.get("/expenses/:month", async (req, res) => {
    const { month } = req.params;
    const regexp = new RegExp("\d\d\d\d-" + month + "-\d\d");
    console.log(regexp);
    const allExpenses = await Expense.find({ date: { $regex: regexp } });
    const allEarnings = await Earning.find({ date: { $regex: regexp } });
    console.log(allExpenses);
    res.status(200).json({
        status: "success",
        results: allExpenses.length,
        data: {
            allExpenses,
            allEarnings
        }
    });

你好，我正在尝试使用regexp过滤出特定月份的数据。它查找没有regexp的数据，但是一旦我把它放进去，它就返回一个空数组。