Get address data of Order
My guess is that one of the orders in the array of orders has a null billingAddress, and the dump you did was for just one of the orders.

If you are going to access the address firstName through the order's billing address, but the address might be null you need to do a check.

You can either do:

{% if order.billingAddress %}
 {{ order.billingAddress.firstName }}
{% endif %}


Or use the null-coalescing operator in twig:

{{ order.billingAddress.firstName ?? '' }}


https://twig.symfony.com/doc/2.x/templates.html#other-operators

Hope that helps.