Fails if production block doesn't exist in database.yml

[seanhuber]

rake aborted!
TypeError: no implicit conversion from nil to integer
/Users/seanhuber/.rvm/gems/ruby-2.3.1@docu_dunk/gems/db-clone-1.1.0/lib/db_clone/db_selections.rb:50:in `[]'
/Users/seanhuber/.rvm/gems/ruby-2.3.1@docu_dunk/gems/db-clone-1.1.0/lib/db_clone/db_selections.rb:50:in `db_prompt'
/Users/seanhuber/.rvm/gems/ruby-2.3.1@docu_dunk/gems/db-clone-1.1.0/lib/db_clone/db_selections.rb:16:in `source_prompt'
/Users/seanhuber/.rvm/gems/ruby-2.3.1@docu_dunk/gems/db-clone-1.1.0/lib/db_clone.rb:17:in `block in clone!'
/Users/seanhuber/.rvm/gems/ruby-2.3.1@docu_dunk/gems/db-clone-1.1.0/lib/db_clone.rb:17:in `each'
/Users/seanhuber/.rvm/gems/ruby-2.3.1@docu_dunk/gems/db-clone-1.1.0/lib/db_clone.rb:17:in `clone!'
/Users/seanhuber/.rvm/gems/ruby-2.3.1@docu_dunk/gems/db-clone-1.1.0/lib/tasks/db_clone_tasks.rake:4:in `block (2 levels) in <top (required)>'
Tasks: TOP => db:clone
(See full trace by running task with --trace)