mark the anonymous_instructor_annotations field as not nullable

closes GRADE-239

test plan:
* Run migrations
* Verify the column is marked not nullable in db/structure.sql

Change-Id: Ib7256d66b764531aec24bbbcac44cdbcbae66ded
Reviewed-on: https://gerrit.instructure.com/130119
Reviewed-by: Neil Gupta <ngupta@instructure.com>
Reviewed-by: Spencer Olson <solson@instructure.com>
Reviewed-by: Cody Cutrer <cody@instructure.com>
Tested-by: Jenkins
QA-Review: Spencer Olson <solson@instructure.com>
Product-Review: Keith T. Garner <kgarner@instructure.com>

db/migrate/20171018160406_mark_assignment_anonymous_instructor_annotations_not_nullable.rb

@@ -0,0 +1,32 @@
+#
+# Copyright (C) 2017 - present Instructure, Inc.
+#
+# This file is part of Canvas.
+#
+# Canvas is free software: you can redistribute it and/or modify it under
+# the terms of the GNU Affero General Public License as published by the Free
+# Software Foundation, version 3 of the License.
+#
+# Canvas is distributed in the hope that it will be useful, but WITHOUT ANY
+# WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR
+# A PARTICULAR PURPOSE. See the GNU Affero General Public License for more
+# details.
+#
+# You should have received a copy of the GNU Affero General Public License along
+# with this program. If not, see <http://www.gnu.org/licenses/>.
+#
+#
+class MarkAssignmentAnonymousInstructorAnnotationsNotNullable < ActiveRecord::Migration[5.0]
+  tag :postdeploy
+
+  def up
+    # In case we missed something in 20170824064214_backfill_assignment_anonymous_instructor_annotations.rb
+    DataFixup::BackfillNulls.run(Assignment, :anonymous_instructor_annotations, default_value: false)
+
+    change_column_null :assignments, :anonymous_instructor_annotations, false
+  end
+
+  def down
+    change_column_null :assignments, :anonymous_instructor_annotations, true
+  end
+end