Warnings when viewing default currency

When viewing the current default currency, and the default is also the conversion source, I'm now seeing lots of warnings like the following:

Notice: Undefined index: GBP in Drupal\commerce_currency_resolver\CurrencyHelper::priceConversion() (line 184 of modules/contrib/commerce_currency_resolver/src/CurrencyHelper.php).
Drupal\commerce_currency_resolver\CurrencyHelper::priceConversion(Object, 'GBP') (Line: 90)
Drupal\commerce_shipping\ShipmentOrderProcessor->process(Object) (Line: 155)
Drupal\commerce_order\OrderRefresh->refresh(Object) (Line: 92)
Drupal\commerce_order\OrderStorage->doPreSave(Object) (Line: 389)
Drupal\Core\Entity\EntityStorageBase->save(Object) (Line: 820)
Drupal\Core\Entity\Sql\SqlContentEntityStorage->save(Object) (Line: 391)
Drupal\Core\Entity\Entity->save() (Line: 114)
Drupal\commerce_order\OrderStorage->postLoad(Array) (Line: 249)
Drupal\Core\Entity\EntityStorageBase->loadMultiple(Array) (Line: 231)
Drupal\commerce_cart\CartProvider->loadCartData(Object) (Line: 184)
Drupal\commerce_cart\CartProvider->getCartIds(NULL) (Line: 172)
Drupal\commerce_cart\CartProvider->getCarts() (Line: 221)
Drupal\commerce_cart\Plugin\Block\CartBlock->getCacheTags() (Line: 86)
Drupal\block\BlockViewBuilder->viewMultiple(Array, 'full', NULL) (Line: 71)
Drupal\block\BlockViewBuilder->view(Object) (Line: 151)
Drupal\block\Plugin\DisplayVariant\BlockPageVariant->build() (Line: 259)
Drupal\Core\Render\MainContent\HtmlRenderer->prepare(Array, Object, Object) (Line: 117)
Drupal\Core\Render\MainContent\HtmlRenderer->renderResponse(Array, Object, Object) (Line: 90)
Drupal\Core\EventSubscriber\MainContentViewSubscriber->onViewRenderArray(Object, 'kernel.view', Object)
call_user_func(Array, Object, 'kernel.view', Object) (Line: 111)
Drupal\Component\EventDispatcher\ContainerAwareEventDispatcher->dispatch('kernel.view', Object) (Line: 156)
Symfony\Component\HttpKernel\HttpKernel->handleRaw(Object, 1) (Line: 68)
Symfony\Component\HttpKernel\HttpKernel->handle(Object, 1, 1) (Line: 57)
Drupal\Core\StackMiddleware\Session->handle(Object, 1, 1) (Line: 47)
Drupal\Core\StackMiddleware\KernelPreHandle->handle(Object, 1, 1) (Line: 47)
Drupal\Core\StackMiddleware\ReverseProxyMiddleware->handle(Object, 1, 1) (Line: 52)
Drupal\Core\StackMiddleware\NegotiationMiddleware->handle(Object, 1, 1) (Line: 23)
Stack\StackedHttpKernel->handle(Object, 1, 1) (Line: 666)
Drupal\Core\DrupalKernel->handle(Object) (Line: 19)