Document attachment - NULL value insertion

Hi all,
I want to add file attachment field in my registration form in Flow Studio, but the user can add attachment in the form or later.
So in that case, there will be an occasion of empty attachment in my form. On that time I’m getting error in the BLOB column in DB.
I have attached error screenshot below, kindly refer and provide any possible solution.


Thanka in advance!!
Swetha B