cart.lastTransaction throws TypeError

[mrksmts]

Description

When the cart is empty and you call cart.lastTransaction in your Twig template you get the following error:

Argument 1 passed to craft\commerce\services\Transactions::getAllTransactionsByOrderId() must be of the type integer, null given, called in /app/vendor/craftcms/commerce/src/elements/Order.php on line 1460

Steps to reproduce

1. Make sure your cart is empty
2. Put {{ cart.lastTransaction }} in your template

Additional info

• Craft version: 3.0.29
• PHP version: 7.1.22
• Database driver & version: MySQL 5.7.24
• Plugins & versions:
  -- Control Panel CSS 2.1.0
  -- Cookies 1.1.10
  -- CP Field Inspect 1.0.5
  -- Craft Commerce 2.0.0-beta.13.1
  -- Element API 2.5.4
  -- Embedded Assets 1.0.2
  -- Expanded Singles 1.0.5
  -- Inlin 2.1.1
  -- MultiSafepay for Craft Commerce 1.0.0
  -- Neo dev-dev-3-port
  -- Redactor 2.1.6
  -- Social 2.0.0-beta.14
  -- Super Table 2.0.11
  -- Typed link field 1.0.15
  -- Video Embedder 1.1.1
  -- Width Fieldtype 1.0.6