added validation

app/models/candidate.rb

 class Candidate < ActiveRecord::Base
+
+	        validates :first_name, presence: true
+	        validates :last_name, presence: true
+ 
+
 	        belongs_to :position
 	        has_many :votes
+
+
 	        
 	    def full_name
 	    	"#{ self.first_name } #{ self.last_name }"

app/models/user.rb

 class User < ActiveRecord::Base
   # Include default devise modules. Others available are:
   # :confirmable, :lockable, :timeoutable and :omniauthable
+  
   devise :database_authenticatable, :registerable,
          :recoverable, :rememberable, :trackable, :validatable
   has_many :votes