Updated app/models/question_option.rb.

Changes:
 - added Answer Identifiers.

Author: John Pinto

app/models/question_option.rb

@@ -11,6 +11,7 @@
 #  created_at  :datetime
 #  updated_at  :datetime
 #  question_id :integer
+#  answer_identifier :string
 #
 # Indexes
 #
@@ -51,6 +52,9 @@ class QuestionOption < ApplicationRecord
 
   validates :is_default, inclusion: { in: BOOLEAN_VALUES,
                                       message: INCLUSION_MESSAGE }
+  
+  validates :answer_identifier, presence: true, allow_blank: true
+
 
   # =============
   # = Callbacks =