我对 javascript 还很陌生，想尝试使用 Google 电子表格和邮件中的邮件合并功能。我复制了教程脚本并做了一些必要的更改（至少我能想到的）。但是当我尝试运行脚本时，出现了 TypeError：无法从 null 读取属性“length”。（第 43 行）

上面提到的第 43 行是下面的 for 循环。有人能帮我告诉我需要修复什么才能运行脚本吗？

// Replaces markers in a template string with values define in a JavaScript data object.
// Arguments:
//   - template: string containing markers, for instance ${"Column name"}
//   - data: JavaScript object with values to that will replace markers. For instance
//     data.columnName will replace marker ${"Column name"}
// Returns a string without markers. If no data is found to replace a marker, it is
// simply removed.
function fillInTemplateFromObject(template, data) {
    var email = template;
    // Search for all the variables to be replaced, for instance ${"Column name"}
    var templateVars = template.match(/\$\{\"[^\"]+\"\}/g);
    // Replace variables from the template with the actual values from the data object.
    // If no value is available, replace with the empty string.
    for (var i = 0; i < templateVars.length; ++i) {
        // normalizeHeader ignores ${"} so we can call it directly here.
        var variableData = data[normalizeHeader(templateVars[i])];
        email = email.replace(templateVars[i], variableData || "");
    }
    return email;
}