Hello Saeed,
From exception it is pretty clear that what is the error →
Caused by: java.lang.IllegalArgumentException: Left and right hand side of binary expression should not be empty
It is happening because of $Date is empty or NULL
Looking at your screenshots I think it is microflow design issue.
In your first check where you have added empty check after that you have added joined so in case of empty
$Date also it is going ahead for next Start Date>= Today check where it is failing, Ideally it should not happen.
I suggest after your empty check do not add join, just add an end event after show validation message.
I hope this will solve your issue.