Cannot insert Value NULL into column

Hi Experts,

I am a student and this is my first time posting ever!  I am doing my DB final and keep getting the error "Cannot insert the value NULL into column "Supplier$" the column does not allow NULLS.  I have googled and checked everything I can think of.  The create table statement I wrote does not allow for Nulls and there are no empty or null columns in the data.  I am trying to save this to a diagram and simply make a relationship with another table.  Ideas? 

Thank you for any and all help.