Make sure that the right data is present.

Otherwise this can throw "NoMethodError - undefined method `[]' for nil:NilClass - /opt/aws/opsworks/releases/20131015111601_209/cookbooks/deploy/recipes/mysql.rb:5:in `from_file'" errors when you've got multiple applications running on one stack, and are using custom JSON to override the deploy recipe for one of them (node[:deploy] will have multiple apps, but only one of them will contain all the necessary information for the deployment).