收到错误TypeError：无法调用null的方法“ getLastColumn”。 （第15行，文件“代码”）

Question

我正在使用Google表格，并且在保存“目标范围的坐标超出了表格尺寸”时收到了错误消息。我检查了脚本，问题出在第15行。这是错误“ TypeError：无法调用null的方法“ getLastColumn”。（第15行，文件“代码”）”如何解决此问题？

function clear() {
   var sheet = SpreadsheetApp.getActive().getSheetByName('Form'); // Change to your Sheet tab name
  sheet.getRange('D11:G35').clearContent(); // Change to the range you would like to clear
  sheet.getRange('C3:C7').clearContent();
}

function save(){
  var source_sheet = SpreadsheetApp.getActive().getSheetByName('Form');
  var agent_name= source_sheet.getRange('C3').getValue();
  var dest_sheet = SpreadsheetApp.getActive().getSheetByName(agent_name);
  //add x number of new columns each save
  var head_data = source_sheet.getRange('B3:E7');
  var body_data = source_sheet.getRange('B9:G35'); //change this range as needed for new scoring parameters

  var col = dest_sheet.getLastColumn(); + 1;
  var dest_data = dest_sheet.getRange(1, col);

  head_data.copyTo(dest_data, {contentsOnly: true});

  dest_data = dest_sheet.getRange(6, col);
  body_data.copyTo(dest_data, {contentsOnly:true});

}

function create_agent_sheets(){
  var agent_sheet = SpreadsheetApp.getActive().getSheetByName("Agents");
  var row = 1;
  var col = 1;
    while(!agent_sheet.getRange(row, col).isBlank()){
      var cell = agent_sheet.getRange(row,col);
      var name = cell.getValue();
      SpreadsheetApp.getActive().insertSheet(name);
      row++;
    }
  agent_sheet.activate();
}

function delete_agent_sheets(){
    var agent_sheet = SpreadsheetApp.getActive().getSheetByName("Agents");
  var row = 1;
  var col = 1;
    while(!agent_sheet.getRange(row, col).isBlank()){
      var cell = agent_sheet.getRange(row,col);
      var name = cell.getValue();
      var sheet = SpreadsheetApp.getActive().getSheetByName(name);
      SpreadsheetApp.getActive().deleteSheet(sheet);
      row++;
    }
  agent_sheet.activate();
}

The error is preventing me from Saving the document.