window form application and varbinary datatype

hi, am beginner in c# and visual studio

i create a windowform application but i don't use a classes in my project ,am just using  forms but in my conception phase i have declared a classes!so is that normal??

second question i have a formular for add a new article but some articles don't have some documents and when i insert a null value i have an error message"the path can not be null,the type of parameter : path"