change required option privacy to optional

app/controllers/collections_controller.rb

 class CollectionsController < ApplicationController
   before_action :set_collection, only: [:show, :update, :destroy, :like, :add_learning_object]
-  before_action :authenticate_user!, only: [:show, :update, :destroy, :like, :add_learning_object]
+  before_action :authenticate_user!, only: [:update, :destroy, :like, :add_learning_object]
 
   # GET /collections
   # GET /collections.json

app/models/collections/context.rb

@@ -6,7 +6,7 @@ module Collections
     end
 
     def privacy
-      raise NotImplementedError, 'This method must be implemented'
+      nil
     end
 
   end

app/repositories/orient_db/collection_repository.rb

@@ -48,7 +48,8 @@ module OrientDb
     ##
     # Select all collections in context
     def all(context = Collections::PublicContext.new)
-      query = sprintf("select * from %s where name<>'Bookmarks' and privacy = '%s'", context.from, context.privacy)
+      query = sprintf("select * from %s where name<>'Bookmarks'", context.from)
+      query += sprintf("and privacy = '%s'", context.privacy) unless context.privacy.blank?
       build_objects connection.query(query)
     end