if coauthor not in coauthor db then it will be add in db

app/models/user/co_author.rb

@@ -9,11 +9,12 @@ class CoAuthor
   field :type
 
 
-  VALID_EMAIL_REGEX = /\A[\w+\-.]+@[a-z\d\-.]+\.[a-z]+\z/i
+  VALID_EMAIL_REGEX = /\A[\w+\-.]+@[a-z\d\-.]+\.[a-z]+\z/
   validates :email, format: { with: VALID_EMAIL_REGEX },
+            allow_blank: true,
              uniqueness: { case_sensitive: false }
 
   validates :co_author, presence: true
-  before_save { |coauthor| coauthor.email = email.downcase }
+  before_save { |coauthor| coauthor.email = email.downcase if not coauthor.email.nil?}
 end