def solved_keys
      if Array === env
        versions = env.map { |single_env| single_env["application_version"] }
      else
        versions = env["application_version"]
      end

      if versions && backtrace && backtrace.length > 0
        versions = [versions] if String === versions

        versions.map do |version|
          Digest::SHA1.hexdigest "#{version} #{backtrace}"
        end
      end
    end
def solved_keys
      if Array === env
        versions = env.map { |single_env| single_env["application_version"] }
      else
        versions = env["application_version"]
      end

      if versions && backtrace && backtrace.length > 0
        versions = [versions] if String === versions

        versions.map do |version|
          Digest::SHA1.hexdigest "#{version} #{backtrace}"
        end
      end
    end
todo - memoize?