Heroku requires Postgresql, gem ‘pg’

Ran into an annoying chicken/egg involving deploying to Heroku with a shared database. It seems that Heroku isn’t happy unless you have gem ‘pg’ in your Gemfile. If you are using the shared database and fail to have gem ‘pg’ in your Gemfile, you app actually deploys OK on Heroku but then generates an Application Error when you call a page. If you check the heroku logs you see something like this: