我按照这里给出的教程编写了一个脚本来从谷歌表格发送电子邮件，但收到以下错误。这里的问题可能是什么？
错误：TypeError: Cannot call method "getRange" of null. (line 7, file "Code")
我的脚本如下：
function sendEmails() {
var sheet = SpreadsheetApp.getActiveSheet();
var startRow = 2; // First row of data to process
var numRows = 2; // Number of rows to process
// Fetch the range of cells A2:B3
var dataRange = sheet.getRange(startRow, 1, numRows, 2)
// Fetch values for each row in the Range.
var data = dataRange.getValues();
for (i in data) {
var row = data[i];
var emailAddress = row[0]; // First column
var message = row[1]; // Second column
var subject = "Silvertop Taxi's Training";
MailApp.sendEmail(emailAddress, subject, message);
}
}
// This constant is written in column C for rows for which an email
// has been sent successfully.
var EMAIL_SENT = "EMAIL_SENT";
function sendEmails2() {
var sheet = SpreadsheetApp.getActiveSheet();
var startRow = 2; // First row of data to process
var numRows = 2; // Number of rows to process
// Fetch the range of cells A2:B3
var dataRange = sheet.getRange(startRow, 1, numRows, 3)
// Fetch values for each row in the Range.
var data = dataRange.getValues();
for (var i = 0; i < data.length; ++i) {
var row = data[i];
var emailAddress = row[0]; // First column
var message = row[1]; // Second column
var emailSent = row[2]; // Third column
if (emailSent != EMAIL_SENT) { // Prevents sending duplicates
var subject = "Silvertop Taxi's Training";
MailApp.sendEmail(emailAddress, subject, message);
sheet.getRange(startRow + i, 3).setValue(EMAIL_SENT);
// Make sure the cell is updated right away in case the script is interrupted
SpreadsheetApp.flush();
}
}
}