Updating a Page Param using Observe Field

I am trying to have the user select a drop down, which will then
update a page param, and then have a link on the page use that param.
My problem is that when the user chooses the drop down, the param for
the page is not being updated and the link is not passing the
category_type param.

Error from the development.log

NoMethodError (You have a nil object when you didn’t expect it!
The error occurred while evaluating nil.value=):


Type 1 Type 2 Type 3

<%= observe_field ‘category_type’, :url => {:controller =>
‘categories’, :action => ‘update_category_type’}, :with =>
“‘categoryType=’ + value” %>

<%= link_to ‘Select’, :controller => ‘categories’, :action =>
‘choose_category’, :id => category, :category_type =>
params[:category_type_link] %>

def update_category_type
render :update do |page|
params[:category_type_link].value = “yikes”