Ruby on Rails : Advance search, undefined method [ ] for nil:Nil class - ruby-on-rails

Question

I am very new to rails and try to make an advance search form which takes two values 'blood_group' and 'area' and based upon that search the records from the database are fetched and will display on the same page (find.html.erb)
I have tried something in find.html.erb but there is an error occurred 'undefined method [] for nil:Nil class' where my search form exists. please help to get out of this error.
Here is my search form in find.html.erb
<%= form_tag find_path , method: :get do %>
<p> <%= label_tag :blood_group %><br />
<%= select_tag (:blood_group), options_for_select(%w[ A+ B+ O+ AB+ A- B- O- AB-]), params[:blood_group] %> </p>
<p> <%= label_tag :area %><br />
<%= select_tag (:area), options_for_select(%w[Indore Vijay_Nagar Bhawar_Kuwa Rajendra_Nagar Geeta_Bhawan Aerodram Tejaji_Nagar Raj_Mohalla Rajwada Chandan_Nagar Gandhi_Nagar Arvindo MY Bombay_Hospital]) , params[:area] %> </p>
<%= submit_tag "Search" , class: "btn btn-primary" , name: nil %>
<% end %>
The error is at the lines where I used select tag.
below is my find action in Donor controller
def find
#donors = Donor.search(params[:blood_group], params[:area]).all
end
And Donor.rb is as follows
class Donor < ActiveRecord::Base
def self.search(blood_group, area)
return all unless blood_group.present? || area.present?
where(['blood_group LIKE ? AND area LIKE ?', "%#{blood_group}%", "%#{area}%"])
end
end

Answer 1

Your search form must be like this:
<%= form_tag find_path , method: :get, remote: true do %>
<p> <%= label_tag :blood_group %><br />
<%= select_tag (:blood_group), options_for_select(%w[ A+ B+ O+ AB+ A- B- O- AB-]) %> </p>
<p> <%= label_tag :area %><br />
<%= select_tag (:area), options_for_select(%w[Indore Vijay_Nagar Bhawar_Kuwa Rajendra_Nagar Geeta_Bhawan Aerodram Tejaji_Nagar Raj_Mohalla Rajwada Chandan_Nagar Gandhi_Nagar Arvindo MY Bombay_Hospital]) %> </p>
<%= submit_tag "Search" , class: "btn btn-primary" , name: nil %>
<% end %>
Modify your controller as:
def find
#donors = Donor.search(params[:blood_group], params[:area]).all
respond_to do |format|
format.js
end
end
Then add find.js.erb to show the searched content.