Heroku push rejected, no Cedar-supported app detec

Question

I'm creating a Rails app with Rails 3.1.3:

git init
git remote add heroku <my heroku repo>
git add .
git commit -a -m "First commit"
git push heroku master

Got:

Counting objects: 102, done.
Delta compression using up to 4 threads.
Compressing objects: 100% (86/86), done.
Writing objects: 100% (102/102), 315.47 KiB, done.
Total 102 (delta 3), reused 0 (delta 0)

**-----> Heroku receiving push
 !     Heroku push rejected, no Cedar-supported app detected**

To [e-mail]:electric-dusk-3217.git
 ! [remote rejected] master -> master (pre-receive hook declined)
error: failed to push some refs to <my heroku rep>

Answer 1

I fixed this by making a superficial change to my Gemfile and recommitting. For some reason it wasn't included in my last commit.