Error for undefined method 'underscore'

It appears in my not at all expert opinion, based on the error, that you're trying to call underscore on the class nil. Are you sure the class is initialized and everything is spelled correctly? To be perfectly honest I'm not really a ruby person but I've worked with a couple of OO languages and when I've had errors like this it has come from making calls to uninitialized objects.

I could be wrong, it could be ruby specific, but it looks like a generic OO bug.

Thank you for the reply Patrick, I'll go back and check for misspelling and so forth.

Here is the error I'm getting

 1) Error:
test_should_get_index(ActivitiesControllerTest):
NoMethodError: undefined method `friends' for nil:NilClass
/Users/justinlicata/Documents/ruby/gnaarly/treebook/app/controllers/activities_controller.rb:3:in `index'

Sorry man, as I said I'm none too good with Ruby. I'm a Java and Obj-C guy. I haven't had a chance to dive into the Treebook project yet so I'm afraid I can't offer up any other suggestions. I'm sure someone around here will know what's up. More importantly than spelling though check for initialization of objects.

i have the same problem

I am also having this problem. Activities are created, but the targetable_type does not get set. So the Activity exists, can be displayed in the view, etc., but when I try to do something with the targetable_type, it of course fails.

Here is what an Activity looks like once it is created (in the console):

<Activity id: 2, user_id: 17, action: "created", targetable_id: nil, targetable_type: nil, created_at: "2015-12-08 05:16:46", updated_at: "2015-12-08 05:16:46">

Activities controller:

class ActivitiesController < ApplicationController
  def index
    following_ids = current_user.following.map(&:id)
    @activities = Activity.where("user_id in (?)", following_ids.push(current_user.id)).order("created_at desc").all
  end
end

Activity Model:

class Activity < ActiveRecord::Base
  belongs_to :user
  belongs_to :targetable, polymorphic: true
end

An example of an Activity creation in another controller:

def create
  @list = current_user.lists.build(list_params)
  if @list.save
    current_user.create_activity(@status, 'created')
    redirect_to root_url
    flash[:success] = "Your grocery list is being created."
  else
    render 'new'
  end
end

I am midway through the Displaying Activity video. I appreciate any help, thank you!