Why can't I enter a NULL value using Numeric or Date type in Postgresql?

[Qzyhwipbsnzad]

I'm doing a little application for the work and it includes a form. When the person using the form doesn't put a value in a data type "numeric" (lets say a PIN number) or even a date in one of my "date" Data Type fields (lets say his anniverssary), it returns me with the errors as follow:Error Type