Ruby On Rails "undefined method `description' for #" when save - forms

Question

I'm relatively new to rails and I've been struggling with this for a couple of days. I'd be much appreciated if you can see where I've gone wrong.
I got this error message
undefined method `description' for #<Invoicegeneric:0x000001054900b0>
if #invoicegeneric.save ==> error at this
response = "Success"
else
response = "Error"
and this is my controller code
def addgenericitems
#invoicegeneric = Invoicegeneric.new
#invoicegeneric.invoice_id = params[:invoice_id]
#invoicegeneric.po_id = params[:po_id]
if #invoicegeneric.save
response = "Success"
else
response = "Error"
end
render :json => {:html => render_to_string(:partial => "invoices/invoicegenerics", :layout => false) }.to_json, :status => :ok
end
and this is my html
<form id="modal-form" class="pure-form pure-form-stacked"
name="invoicegenericform" action="<%= addgenericitems_invoice_path(#invoice) %>"
method="post">
<fieldset>
<label for="po_id">PO</label>
<select name="po_id" class="chzn-select">
<% Purchaseorder.active.order(:sku).each do |p| %>
<option value="<%= p.sku %>"><%= "#{p.sku}" %></option>
<% end %>
</select>
</fieldset>
<fieldset>
<label for="sku_sj">SJ</label>
<input name="sku_sj" type="text">
</fieldset>
<div class="modal-footer">
<button class="pure-button" data-dismiss="modal" aria-hidden="true">Close</button>
<input type="submit" class="pure-button pure-button-primary" value="Tambah"/>
</div>
</form>
In my table there is no column name description