在写外来对象组件操作过程中，有时对调用的方法中不用的参数调用Null错误，填充此参数即可。
Excel.Workbook wb = ThisApplication.Workbooks.Open(@"c:\YourPath\YourWorkbook.xls", Type.Missing, Type.Missing, Type.Missing, Type.Missing, Type.Missing, Type.Missing, Type.Missing, Type.Missing, Type.Missing, Type.Missing, Type.Missing, Type.Missing, Type.Missing, Type.Missing);