Call to a member function get_stock_managed_by_id() on null in class-wc-cart.php

Hi All,

I am currently experiencing a fatal error in my log:
PHP Fatal error: Call to a member function get_stock_managed_by_id() on null in /var/www/clients/client10/web11/web/2016/wp-content/plugins/woocommerce/includes/class-wc-cart.php on line 434

When on the checkout page, i hit ‘Proceed to Payment’ or ‘Pay for Order’ and i get an ‘Internal Server Error’ in the Woocommerce error box at the top of page. The log displays the above Fatal Error. Not sure what this is being caused by, but if you could point me in the right direction. Thank you!

Here is my status:

### WordPress Environment ###

Home URL: https://caisafety.com/2016
Site URL: https://caisafety.com/2016
WC Version: 3.0.8
Log Directory Writable: ?
WP Version: 4.8
WP Multisite: –
WP Memory Limit: 256 MB
WP Debug Mode: ?
WP Cron: ?
Language: en_US

### Server Environment ###

Server Info: Apache/2.4.10 (Debian)
PHP Version: 5.6.30-0+deb8u1
PHP Post Max Size: 64 MB
PHP Time Limit: 30
PHP Max Input Vars: 1000
cURL Version: 7.38.0
OpenSSL/1.0.1t

SUHOSIN Installed: –
MySQL Version: ? 5.5.55 - We recommend a minimum MySQL version of 5.6. See: WordPress requirements
Max Upload Size: 64 MB
Default Timezone is UTC: ?
fsockopen/cURL: ?
SoapClient: ?
DOMDocument: ?
GZip: ?
Multibyte String: ?
Remote Post: ?
Remote Get: ?

### Database ###

WC Database Version: 3.0.8
WC Database Prefix: wpsite_
woocommerce_sessions: ?
woocommerce_api_keys: ?
woocommerce_attribute_taxonomies: ?
woocommerce_downloadable_product_permissions: ?
woocommerce_order_items: ?
woocommerce_order_itemmeta: ?
woocommerce_tax_rates: ?
woocommerce_tax_rate_locations: ?
woocommerce_shipping_zones: ?
woocommerce_shipping_zone_locations: ?
woocommerce_shipping_zone_methods: ?
woocommerce_payment_tokens: ?
woocommerce_payment_tokenmeta: ?

### Security ###

Secure connection (HTTPS): ?
Hide errors from visitors: ?

### Active Plugins (26) ###

Accordion Slider: by bqworks – 1.5.0
Add Meta Tags: by George Notaras – 2.11.3
Contact Form 7: by Takayuki Miyoshi – 4.8
Custom Field Suite: by Matt Gibbs – 2.5.9
Duplicate Page: by mndpsingh287 – 2.3
Enable Media Replace: by M?ns Jonasson – 3.0.6
WPBakery Visual Composer: by Michael M - WPBakery.com – 5.1.1
MailChimp for WooCommerce: by MailChimp – 2.0.0
New RoyalSlider: by Dmitry Semenov – 3.3.4
Scripts n Styles: by unFocus Projects – 3.4.0
Search By SKU - for Woocommerce: by Matthew Lawson – 0.6.1
Select Core: by Select Themes – 1.3.1
Select Twitter Feed: by Select Themes – 1.0
Simple Sales Tax: by Simple Sales Tax – 5.2
Booster Plus for WooCommerce: by Algoritmika Ltd – 1.1.0
Woocommerce CSV import variable products: by Allaerd Mensonides – 3.0.1
Woocommerce CSV Import: by Allaerd Mensonides – 3.3.5
WooCommerce FedEx Drop Shipping Pro: by IgniteWoo.com – 2.2.13
WooCommerce PayPal Powered by Braintree Gateway: by WooCommerce – 2.0.3
Booster for WooCommerce: by Algoritmika Ltd – 2.8.2
Woocommerce quotation: by Aldaba Digital – 2.6.5
WooCommerce UPS Drop Shipping Pro: by IgniteWoo.com - Custom Add-ons for WooCommerce! – 2.4
WooCommerce: by Automattic – 3.0.8
WooCommerce Helper: by WooCommerce – 1.7.2 – Network enabled
Wordfence Security: by Wordfence – 6.3.11
YITH WooCommerce Wishlist: by YITHEMES – 2.1.2

### Settings ###

API Enabled: ?
Force SSL: –
Currency: USD ($)
Currency Position: left
Thousand Separator: ,
Decimal Separator: .
Number of Decimals: 2
Taxonomies: Product Types: bundle (bundle)
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: #5998 - /fall-protection-store/
Cart: #5990 - /cart/
Checkout: #5992 - /checkout/
My account: #5996 - /my-account/

### Theme ###

Name: Startit
Version: 2.3
Author URL: https://themeforest.net/user/select-themes
Child Theme: ? – If you're modifying WooCommerce on a parent theme you didn't build personally
then we recommend using a child theme. See: How to create a child theme

WooCommerce Support: ?

### Templates ###

Archive Template: Your theme has a woocommerce.php file
you will not be able to override the woocommerce/archive-product.php custom template since woocommerce.php has priority over archive-product.php. This is intended to prevent display issues.

Overrides: startit/woocommerce/cart/cart-shipping.php
startit/woocommerce/cart/cart-totals.php
startit/woocommerce/cart/cart.php
startit/woocommerce/cart/shipping-calculator.php
startit/woocommerce/checkout/form-billing.php
startit/woocommerce/checkout/form-pay.php
startit/woocommerce/checkout/form-shipping.php
startit/woocommerce/checkout/review-order.php
startit/woocommerce/checkout/terms.php
startit/woocommerce/checkout/thankyou.php
startit/woocommerce/content-product.php
startit/woocommerce/content-single-product.php
startit/woocommerce/content-widget-product.php
startit/woocommerce/emails/customer-completed-order.php
startit/woocommerce/emails/customer-new-account.php
startit/woocommerce/emails/customer-note.php
startit/woocommerce/emails/customer-processing-order.php
startit/woocommerce/emails/customer-refunded-order.php
startit/woocommerce/emails/email-addresses.php
startit/woocommerce/emails/email-customer-details.php
startit/woocommerce/emails/email-header.php
startit/woocommerce/emails/email-order-details.php
startit/woocommerce/emails/email-order-items.php
startit/woocommerce/emails/email-styles.php
startit/woocommerce/global/form-login.php
startit/woocommerce/global/quantity-input.php
startit/woocommerce/loop/loop-start.php
startit/woocommerce/myaccount/dashboard.php
startit/woocommerce/myaccount/my-address.php
startit/woocommerce/myaccount/view-order.php
startit/woocommerce/notices/notice.php
startit/woocommerce/order/order-details-item.php
startit/woocommerce/order/order-details.php
startit/woocommerce/single-product/add-to-cart/external.php
startit/woocommerce/single-product/add-to-cart/simple.php
startit/woocommerce/single-product/add-to-cart/variable.php
startit/woocommerce/single-product/add-to-cart/variation.php
startit/woocommerce/single-product/meta.php
startit/woocommerce/single-product/price.php
startit/woocommerce/single-product/product-image.php
startit/woocommerce/single-product/product-thumbnails.php
startit/woocommerce/single-product/related.php
startit/woocommerce/single-product/share.php
startit/woocommerce/single-product/tabs/tabs.php

### Braintree (Credit Card) ###

Environment: Sandbox
Tokenization Enabled: 
Debug Mode: Save to Log