错误:“;发送电子邮件失败:没有收件人"

运行以下代码时出现错误：

发送电子邮件失败：没有收件人

这是正在运行或谷歌电子表格。我假设它会在电子邮件地址列中查找电子邮件地址，在读取最后一个后，它会转到下一个空白单元格，但没有看到任何内容，然后给出一个错误。

如果是这种情况，当它转到列中的最后一个时，我如何让它停止查找电子邮件地址？

错误在第18行：MailApp.sendEmail(emailAddress, subject, message);

    var EMAIL_SENT = "EMAIL_SENT";
function sendEmails2() {
  var ss = SpreadsheetApp.getActiveSpreadsheet();
  var sheets = ss.getSheets();
  var startRow = 2;  
  var numRows = 1000;
  var sheet = ss.getSheetByName ('Administrators')
  var dataRange = sheet.getRange(startRow, 1, numRows, sheet.getLastColumn());
  var data = dataRange.getValues();
  for (var i = 0; i < data.length; ++i) {
    var row = data[i];
    var emailAddress = row[1]; 
    var message = row[28];       
    var emailSent = row[29]; 
    if (emailSent != EMAIL_SENT) {  
      var subject = "Tuition Reimbursement Status";
      MailApp.sendEmail(emailAddress, subject, message);
      sheet.getRange(startRow + i, 30).setValue(EMAIL_SENT);

     var sheet = ss.getSheetByName ('Teachers')
     var dataRange = sheet.getRange(startRow, 1, numRows, sheet.getLastColumn());
     var data = dataRange.getValues();
     for (var i = 0; i < data.length; ++i) {
     var row = data[i];
     var emailAddress = row[1]; 
     var message = row[28];       
     var emailSent = row[29]; 
     if (emailSent != EMAIL_SENT) {  
       var subject = "Tuition Reimbursement Status";
       MailApp.sendEmail(emailAddress, subject, message);
       sheet.getRange(startRow + i, 30).setValue(EMAIL_SENT);

     var sheet = ss.getSheetByName ('Support Staff')
     var dataRange = sheet.getRange(startRow, 1, numRows, sheet.getLastColumn());
     var data = dataRange.getValues();
     for (var i = 0; i < data.length; ++i) {
     var row = data[i];
     var emailAddress = row[1]; 
     var message = row[28];       
     var emailSent = row[29]; 
     if (emailSent != EMAIL_SENT) {  
       var subject = "Tuition Reimbursement Status";
       MailApp.sendEmail(emailAddress, subject, message);
       sheet.getRange(startRow + i, 30).setValue(EMAIL_SENT);

      SpreadsheetApp.flush();
      }
     }
    }
   }
  }
 }
}