Hello there! Have you considered - Supreme Panic Magic (Have a quick look on google cant remember the place now)? Ive heard some interesting things about it and my mate said good bye the anxiety problem with it.
Love your tutorials but I do know of a field can and should have null ability. One example is Address2 If you don't have an apartment number or suit, there is no need for that field to be populated. Another might be MiddleInit. Not every one has a middle name. The examples could go on quite detailed but it is a needed function. Keep up the good work.
null filed means that they CAN be empty (they are null by default)
so when you creating some form in php with optional fields, values inputed by user can be empty and no error will apper when he press sumbit button because database does not require value in this field