Redmine

Redmine-3.3.1、ruby 2.3.1p112、sqlserver2014.
run commond：db:migrate
errors as flow:

20160404080304 ForcePasswordResetDuringSetup: migrating ==================
20160404080304 ForcePasswordResetDuringSetup: migrated (0.0126s) ========= 20160416072926 RemovePositionDefaults: migrating =========================
-- change_column("boards", :position, :integer, {:default=>nil})
> 0.0541s
- change_column("custom_fields", :position, :integer, {:default=>nil})
rake aborted!
StandardError: An error has occurred, this and all later migrations canceled:

undefined method `type' for nil:NilClass/opt/redmine-3.3.1/db/migrate/20160416072926_remove_position_defaults.rb:4:in `block in up'
/opt/redmine-3.3.1/db/migrate/20160416072926_remove_position_defaults.rb:3:in `each'
/opt/redmine-3.3.1/db/migrate/20160416072926_remove_position_defaults.rb:3:in `up'
NoMethodError: undefined method `type' for nil:NilClass
/opt/redmine-3.3.1/db/migrate/20160416072926_remove_position_defaults.rb:4:in `block in up'
/opt/redmine-3.3.1/db/migrate/20160416072926_remove_position_defaults.rb:3:in `each'
/opt/redmine-3.3.1/db/migrate/20160416072926_remove_position_defaults.rb:3:in `up'
Tasks: TOP => db:migrate
(See full trace by running task with --trace)

the content of 20160416072926_remove_position_defaults.rb is:

class RemovePositionDefaults < ActiveRecord::Migration
  def up
    [Board, CustomField, Enumeration, IssueStatus, Role, Tracker].each do |klass|
      change_column klass.table_name, :position, :integer, :default => nil
    end
  end

  def down
    [Board, CustomField, Enumeration, IssueStatus, Role, Tracker].each do |klass|
      change_column klass.table_name, :position, :integer, :default => 1
    end
  end
end

I delete table CustomField,It's ok and work well.