Input Field is empty and in data base showing null

Input is optional and when i dont fill and procced further, it is showing null in database then on other side submitting bid input field is showing error that you cant enter num more then actual bid.

Welcome to the forum!
I am not experienced to answer this particular question.
However, if you will provide some code, or maybe link to your code, it will be better chance, that someone will provide some help.