why doesn't app.versions get created?

deployable_application.rb

class DeployableApplication < ActiveRecord::Base
  belongs_to :git_repo
  belongs_to :rpm_repo

  has_many :versions
end

git_rpm_builder_engine.rb

class GitRpmBuilderEngine
  require 'tmpdir'

  def initialize(_deployable_application_id, _major=false, _minor=false, _micro=true)
    @app = DeployableApplication.find(_deployable_application_id)
    @git_repo = @app.git_repo
    @rpm_repo = @app.rpm_repo
    @major = _major
    @minor = _minor
    @micro = _micro
    @app_name = @git_repo.name
    @version = get_version
    # does this DeployableApplication have a Version?  (first import)
    unless @app.versions.empty?
p "got to @app.versions builder"
      @app.versions.create(build_version: @version)
    end

version.rb

class Version < ActiveRecord::Base
  belongs_to :deployable_application
end