adding topics validation

Signed-off-by: man13 <man13@inf.ufpr.br>

app/models/learning_object.rb

@@ -18,7 +18,7 @@ class LearningObject < ActiveRecord::Base
   belongs_to :object_type
   belongs_to :attachment, class_name: 'LearningObject::Attachment'
 
-  validates_presence_of :name, :publisher, :object_type, :language, :author
+  validates_presence_of :name, :publisher, :object_type, :language, :author, :topics
   validates :id_dspace, presence: true, uniqueness: true, unless: :is_draft?
 
   default_scope { includes(:object_type, :attachment, :attachments).order(score: :desc) }