## users_controller.rb

  def edit
    @roles = Role.find(:all)
    @user = User.find(params[:id])
  end

  def update
    @user = User.find(params[:id])

    respond_to do |format|
      if @user.update_attributes(params[:user])
        flash[:notice] = "User '#{@user.name}' was successfully updated."
        format.html { redirect_to(@user) }
        format.xml  { head :ok }
      else
        flash[:error]  = "There was a problem updating the user. No users were updated."
        render :action => 'edit'
      end
    end
  end

## error (after submitting with bad password confirmation)

Showing users/edit.html.erb where line #25 raised:

You have a nil object when you didn't expect it!
You might have expected an instance of Array.
The error occurred while evaluating nil.map

Extracted source (around line #25):

22: <%= f.password_field :password_confirmation %></p>
23:
24: <p><%= label_tag 'role' %><br/>
25: <%= collection_select(:user, :role_id, @roles, :id, :name) %></p>
26:
27:
28: <p style="margin-top: 20px"><%= f.submit 'Update' %></p>

## edit.html.erb

<div class="form">
<h1>Edit user</h1>
<% @user.password = @user.password_confirmation = nil %>

<%= error_messages_for :user %>

<% form_for(@user) do |f| %>

<p><%= f.label 'login' %><br/>
<%= f.text_field :login %></p>

<p><%= label_tag 'name' %><br/>
<%= f.text_field :name %></p>

<p><%= label_tag 'email' %><br/>
<%= f.text_field :email %></p>

<p><%= label_tag 'password' %><br/>
<%= f.password_field :password %></p>

<p><%= label_tag 'password_confirmation', 'Confirm Password' %><br/>
<%= f.password_field :password_confirmation %></p>

<p><%= label_tag 'role' %><br/>
<%= collection_select(:user, :role_id, @roles, :id, :name) %></p>


<p style="margin-top: 20px"><%= f.submit 'Update' %></p>
<% end -%>

</div>