TOPIC: Customers able to delete deposit amount

I have setup the minimum partial payment to be $50 so they have the option to pay more. Now, if someone tries to put an amount lower than $50 it gives them an error (yay), but when someone totally deletes the amount and leaves it blank it allows them to proceed without paying a deposit. How can we fix it so that the minimum amount is required?

I am running version 3.0.9

Any help or hint would be helpful.

Thanks!