vba计算两个单元格中日期之间的天数，仅当两个单元格都有日期时才返回值

I have the below code to calculate days between dates in two cells, but it returns an error value if column X has no date. I want the code to only return a value if there is a date in column X, but I don't know how to do that. I am new to VBA. Thanks in advance for any help you can give.I have the below code to calculate days between