rsim/oracle-enhanced — pull request #489 by yahonda (2014-08-31 23:10:13+00:00)
Title: Add `null: true` to avoid DEPRECATION WARNING

This pull request addresses following deprecation warning by setting `null: true`.
```ruby
DEPRECATION WARNING: `timestamp` was called without specifying an option for `null`. In Rails
5.0, this behavior will change to `null: false`. You should manually
specify `null: true` to prevent the behavior of your existing migrations
```