set request_for_comment.solved default to false and set all null values in database for that attribute to false

db/migrate/20170403162848_set_default_for_request_for_comment_solved.rb

@@ -0,0 +1,6 @@
+class SetDefaultForRequestForCommentSolved < ActiveRecord::Migration
+  def change
+    change_column_default :request_for_comments, :solved, false
+    RequestForComment.where(solved: nil).update_all(solved: false)
+  end
+end

db/schema.rb

@@ -11,7 +11,7 @@
 #
 # It's strongly recommended that you check this file into your version control system.
 
-ActiveRecord::Schema.define(version: 20170323130756) do
+ActiveRecord::Schema.define(version: 20170403162848) do
 
   # These are extensions that must be enabled in order to support this database
   enable_extension "plpgsql"
@@ -246,7 +246,7 @@ ActiveRecord::Schema.define(version: 20170323130756) do
     t.datetime "updated_at"
     t.string   "user_type",     limit: 255
     t.text     "question"
-    t.boolean  "solved"
+    t.boolean  "solved",                    default: false
     t.integer  "submission_id"
   end