change_column_null:milestones,:project_id,trueadd_column:milestones,:group_id,:integerenddefdown# We cannot rollback project_id not null constraint if there are records# with null values.execute"DELETE from milestones WHERE project_id IS NULL"remove_column:milestones,:group_idchange_column:milestones,:project_id,:integer,null: falseendend