Call to a member function is_on_sale() on null after updating to 3.4.0

The basket of my store is broken after updating WooCommerce. I’m not overriding any templates and have removed all hooks and filters.

Fatal error: Uncaught Error: Call to a member function is_on_sale() on null in /var/www/XXXXX.co.uk/wp-content/plugins/woocommerce/templates/single-product/sale-flash.php:26 Stack trace: #0 /var/www/XXXXX.co.uk/wp-content/plugins/woocommerce/includes/wc-core-functions.php(209): include() #1 /var/www/XXXXX.co.uk/wp-content/plugins/woocommerce/includes/wc-template-functions.php(1486): wc_get_template(‘single-product/…’) #2 /var/www/XXXXX.co.uk/wp-includes/class-wp-hook.php(286): woocommerce_show_product_sale_flash(”) #3 /var/www/XXXXX.co.uk/wp-includes/class-wp-hook.php(310): WP_Hook->apply_filters(”, Array) #4 /var/www/XXXXX.co.uk/wp-includes/plugin.php(453): WP_Hook->do_action(Array) #5 /var/www/XXXXX.co.uk/wp-content/plugins/woocommerce/templates/content-single-product.php(41): do_action(‘woocommerce_bef…’) #6 /var/www/XXXXX.co.uk/wp-includes/template.php(690): require(‘/var/www/…’) #7 /var/www/XXXXX.co.uk/wp-content/plugins/woocommerce/includes/wc-core-functions.php(178) in /var/www/XXXXX.co.uk/wp-content/plugins/woocommerce/templates/single-product/sale-flash.php on line 26

### WordPress Environment ###

WC Version: 3.4.0
Log Directory Writable: ?
WP Version: 4.9.6
WP Multisite: –
WP Memory Limit: 256 MB
WP Debug Mode: ?
WP Cron: ?
Language: en_GB
External object cache: –

### Server Environment ###

Server Info: Apache/2.4.18 (Ubuntu)
PHP Version: ? 7.0.30-0ubuntu0.16.04.1 - We recommend using PHP version 7.2 or above for greater performance and security. How to update your PHP version
PHP Post Max Size: 8 MB
PHP Time Limit: 30
PHP Max Input Vars: 1000
cURL Version: 7.47.0
OpenSSL/1.0.2g

SUHOSIN Installed: –
MySQL Version: 5.7.22
Max Upload Size: 2 MB
Default Timezone is UTC: ?
fsockopen/cURL: ?
SoapClient: ?
DOMDocument: ?
GZip: ?
Multibyte String: ?
Remote Post: ?
Remote Get: ?

### Database ###

WC Database Version: 3.4.0
WC Database Prefix: wp_
MaxMind GeoIP Database: ?
Total Database Size: 3.93MB
Database Data Size: 2.61MB
Database Index Size: 1.32MB
wp_woocommerce_sessions: Data: 0.02MB + Index: 0.02MB
wp_woocommerce_api_keys: Data: 0.02MB + Index: 0.03MB
wp_woocommerce_attribute_taxonomies: Data: 0.02MB + Index: 0.02MB
wp_woocommerce_downloadable_product_permissions: Data: 0.02MB + Index: 0.05MB
wp_woocommerce_order_items: Data: 0.02MB + Index: 0.02MB
wp_woocommerce_order_itemmeta: Data: 0.02MB + Index: 0.03MB
wp_woocommerce_tax_rates: Data: 0.02MB + Index: 0.06MB
wp_woocommerce_tax_rate_locations: Data: 0.02MB + Index: 0.03MB
wp_woocommerce_shipping_zones: Data: 0.02MB + Index: 0.00MB
wp_woocommerce_shipping_zone_locations: Data: 0.02MB + Index: 0.03MB
wp_woocommerce_shipping_zone_methods: Data: 0.02MB + Index: 0.00MB
wp_woocommerce_payment_tokens: Data: 0.02MB + Index: 0.02MB
wp_woocommerce_payment_tokenmeta: Data: 0.02MB + Index: 0.03MB
wp_woocommerce_log: Data: 0.02MB + Index: 0.02MB
wp_commentmeta: Data: 0.02MB + Index: 0.03MB
wp_comments: Data: 0.02MB + Index: 0.09MB
wp_links: Data: 0.02MB + Index: 0.02MB
wp_options: Data: 0.42MB + Index: 0.05MB
wp_postmeta: Data: 1.52MB + Index: 0.47MB
wp_posts: Data: 0.17MB + Index: 0.06MB
wp_termmeta: Data: 0.02MB + Index: 0.03MB
wp_terms: Data: 0.02MB + Index: 0.03MB
wp_term_relationships: Data: 0.02MB + Index: 0.02MB
wp_term_taxonomy: Data: 0.02MB + Index: 0.03MB
wp_usermeta: Data: 0.02MB + Index: 0.03MB
wp_users: Data: 0.02MB + Index: 0.05MB
wp_wc_download_log: Data: 0.02MB + Index: 0.03MB
wp_wc_webhooks: Data: 0.02MB + Index: 0.02MB

### Post Type Counts ###

acf-field: 39
acf-field-group: 11
attachment: 193
nav_menu_item: 19
page: 9
post: 1
product: 91
product_variation: 10
revision: 42
shop_coupon: 2
shop_order: 1
wpcf7_contact_form: 1

### Security ###

Secure connection (HTTPS): ?
Hide errors from visitors: ?Error messages should not be shown to visitors.

### Active Plugins (5) ###

Advanced Custom Fields PRO: by Elliot Condon – 5.6.7
Regenerate Thumbnails: by Alex Mills (Viper007Bond) – 3.0.2
Simple Page Ordering: by Jake Goldman
10up – 2.3.2

WooCommerce: by Automattic – 3.4.0
WPS Hide Login: by WPServeur
NicolasKulka
tabrisrp – 1.3.4.2

### Settings ###

API Enabled: –
Force SSL: –
Currency: GBP (￡)
Currency Position: left
Thousand Separator: ,
Decimal Separator: .
Number of Decimals: 2
Taxonomies: Product Types: external (external)
grouped (grouped)
simple (simple)
variable (variable)

Taxonomies: Product Visibility: exclude-from-catalog (exclude-from-catalog)
exclude-from-search (exclude-from-search)
featured (featured)
outofstock (outofstock)
rated-1 (rated-1)
rated-2 (rated-2)
rated-3 (rated-3)
rated-4 (rated-4)
rated-5 (rated-5)

### WC Pages ###

Shop base: #48 - /shop/
Cart: #29 - /basket/
Checkout: #30 - /checkout/
My account: #31 - /my-account/
Terms and conditions: #162 - /terms-and-conditions/

### Theme ###

Name: XXXXXX
Version: 1.0
Child Theme: ? – If you are modifying WooCommerce on a parent theme that you did not build personally we recommend using a child theme. See: How to create a child theme
WooCommerce Support: ?

### Templates ###

Overrides: –