ruby on rails RuntimeError in User#new Called id for nil, which would mistakenly be 4 -- if you really wanted the id of nil, use object_id

That is error at object table

look my sintak error

Add Mahasiswa

<% form_for @person do |f| %>
 
    Nama
    <%= f.text_field :nama %>
 
 
 
    Prodi
    <%= f.text_field :prodi %>
 

<% end %>   
TRY

change @person to @mahasiswa

thank