Remove default relative_position value

This makes `epic_issues` consistent with other tables
using our `RelativePositioning` class

db/migrate/20190806071559_remove_epic_issues_default_relative_position.rb

+# frozen_string_literal: true
+
+class RemoveEpicIssuesDefaultRelativePosition < ActiveRecord::Migration[5.2]
+  DOWNTIME = false
+
+  def change
+    change_column_null :epic_issues, :relative_position, true
+    change_column_default :epic_issues, :relative_position, from: 1073741823, to: nil
+  end
+end

db/schema.rb

@@ -10,7 +10,7 @@
 #
 # It's strongly recommended that you check this file into your version control system.
 
-ActiveRecord::Schema.define(version: 2019_08_02_235445) do
+ActiveRecord::Schema.define(version: 2019_08_06_071559) do
 
   # These are extensions that must be enabled in order to support this database
   enable_extension "pg_trgm"
@@ -1194,7 +1194,7 @@ ActiveRecord::Schema.define(version: 2019_08_02_235445) do
   create_table "epic_issues", id: :serial, force: :cascade do |t|
     t.integer "epic_id", null: false
     t.integer "issue_id", null: false
-    t.integer "relative_position", default: 1073741823, null: false
+    t.integer "relative_position"
     t.index ["epic_id"], name: "index_epic_issues_on_epic_id"
     t.index ["issue_id"], name: "index_epic_issues_on_issue_id", unique: true
   end

spec/support/shared_examples/relative_positioning_shared_examples.rb

@@ -17,8 +17,8 @@ RSpec.shared_examples 'a class that supports relative positioning' do
 
   describe '.move_nulls_to_end' do
     it 'moves items with null relative_position to the end' do
-      skip("#{item1} has a default relative position") if item1.relative_position
-      skip("#{item2} has a default relative position") if item2.relative_position
+      item1.update!(relative_position: nil)
+      item2.update!(relative_position: nil)
 
       described_class.move_nulls_to_end([item1, item2])
 
@@ -28,7 +28,7 @@ RSpec.shared_examples 'a class that supports relative positioning' do
     end
 
     it 'moves the item near the start position when there are no existing positions' do
-      skip("#{item1} has a default relative position") if item1.relative_position
+      item1.update!(relative_position: nil)
 
       described_class.move_nulls_to_end([item1])