Error: Call to a member function getFieldStorageDefinition() on null in Drupal\Core\Entity\ContentEntityBase->getEntityKey()

Just evaluating your module (thanks for contributing it!), I have found this error.

Steps: Clean install on 8.8.2 while trying to add the 1st transaction:

http://.../admin/structure/user_points/add
Message   Error: Call to a member function getFieldStorageDefinition() on null in Drupal\Core\Entity\ContentEntityBase->getEntityKey() (line 1303 of /web/core/lib/Drupal/Core/Entity/ContentEntityBase.php)

#0 /web/core/lib/Drupal/Core/Entity/ContentEntityBase.php(1254): Drupal\Core\Entity\ContentEntityBase->getEntityKey('label')
#1 /web/modules/contrib/user_points/src/Form/UserPointsForm.php(38): Drupal\Core\Entity\ContentEntityBase->label()
#2 [internal function]: Drupal\user_points\Form\UserPointsForm->save(Array, Object(Drupal\Core\Form\FormState))
#3 /web/core/lib/Drupal/Core/Form/FormSubmitter.php(112): call_user_func_array(Array, Array)
#4 /web/core/lib/Drupal/Core/Form/FormSubmitter.php(52): Drupal\Core\Form\FormSubmitter->executeSubmitHandlers(Array, Object(Drupal\Core\Form\FormState))
#5 /web/core/lib/Drupal/Core/Form/FormBuilder.php(591): Drupal\Core\Form\FormSubmitter->doSubmitForm(Array, Object(Drupal\Core\Form\FormState))
#6 /web/core/lib/Drupal/Core/Form/FormBuilder.php(320): Drupal\Core\Form\FormBuilder->processForm('user_points_add...', Array, Object(Drupal\Core\Form\FormState))
#7 /web/core/lib/Drupal/Core/Controller/FormController.php(91): Drupal\Core\Form\FormBuilder->buildForm(Object(Drupal\user_points\Form\UserPointsForm), Object(Drupal\Core\Form\FormState))
#8 [internal function]: Drupal\Core\Controller\FormController->getContentResult(Object(Symfony\Component\HttpFoundation\Request), Object(Drupal\Core\Routing\RouteMatch))
#9 /web/core/lib/Drupal/Core/EventSubscriber/EarlyRenderingControllerWrapperSubscriber.php(123): call_user_func_array(Array, Array)
#10 /web/core/lib/Drupal/Core/Render/Renderer.php(573): Drupal\Core\EventSubscriber\EarlyRenderingControllerWrapperSubscriber->Drupal\Core\EventSubscriber\{closure}()
#11 /web/core/lib/Drupal/Core/EventSubscriber/EarlyRenderingControllerWrapperSubscriber.php(124): Drupal\Core\Render\Renderer->executeInRenderContext(Object(Drupal\Core\Render\RenderContext), Object(Closure))
#12 /web/core/lib/Drupal/Core/EventSubscriber/EarlyRenderingControllerWrapperSubscriber.php(97): Drupal\Core\EventSubscriber\EarlyRenderingControllerWrapperSubscriber->wrapControllerExecutionInRenderContext(Array, Array)
#13 /vendor/symfony/http-kernel/HttpKernel.php(151): Drupal\Core\EventSubscriber\EarlyRenderingControllerWrapperSubscriber->Drupal\Core\EventSubscriber\{closure}()
#14 /vendor/symfony/http-kernel/HttpKernel.php(68): Symfony\Component\HttpKernel\HttpKernel->handleRaw(Object(Symfony\Component\HttpFoundation\Request), 1)
#15 /web/core/lib/Drupal/Core/StackMiddleware/Session.php(57): Symfony\Component\HttpKernel\HttpKernel->handle(Object(Symfony\Component\HttpFoundation\Request), 1, true)
#16 /web/core/lib/Drupal/Core/StackMiddleware/KernelPreHandle.php(47): Drupal\Core\StackMiddleware\Session->handle(Object(Symfony\Component\HttpFoundation\Request), 1, true)
#17 /web/core/modules/page_cache/src/StackMiddleware/PageCache.php(106): Drupal\Core\StackMiddleware\KernelPreHandle->handle(Object(Symfony\Component\HttpFoundation\Request), 1, true)
#18 /web/core/modules/page_cache/src/StackMiddleware/PageCache.php(85): Drupal\page_cache\StackMiddleware\PageCache->pass(Object(Symfony\Component\HttpFoundation\Request), 1, true)
#19 /web/core/lib/Drupal/Core/StackMiddleware/ReverseProxyMiddleware.php(47): Drupal\page_cache\StackMiddleware\PageCache->handle(Object(Symfony\Component\HttpFoundation\Request), 1, true)
#20 /web/core/lib/Drupal/Core/StackMiddleware/NegotiationMiddleware.php(52): Drupal\Core\StackMiddleware\ReverseProxyMiddleware->handle(Object(Symfony\Component\HttpFoundation\Request), 1, true)
#21 /vendor/stack/builder/src/Stack/StackedHttpKernel.php(23): Drupal\Core\StackMiddleware\NegotiationMiddleware->handle(Object(Symfony\Component\HttpFoundation\Request), 1, true)
#22 /web/core/lib/Drupal/Core/DrupalKernel.php(694): Stack\StackedHttpKernel->handle(Object(Symfony\Component\HttpFoundation\Request), 1, true)
#23 /web/index.php(19): Drupal\Core\DrupalKernel->handle(Object(Symfony\Component\HttpFoundation\Request))
#24 {main}