Calling assert() with a string argument is deprecated

I've got the following errors in PHP 7.2.0alpha2:

Deprecated function: assert(): Calling assert() with a string argument is deprecated in Drupal\Core\Cache\Cache::mergeContexts() (line 32 of core/lib/Drupal/Core/Cache/Cache.php).
Drupal\Core\Cache\Cache::mergeContexts(Array, Array) (Line: 104)
Drupal\Core\Cache\CacheableMetadata->merge(Object) (Line: 27)
Drupal\Core\Render\BubbleableMetadata->merge(Object) (Line: 677)
Drupal\Core\Render\Renderer->mergeBubbleableMetadata(Array, Array) (Line: 171)
...
Deprecated function: assert(): Calling assert() with a string argument is deprecated in Drupal\Core\Cache\CacheCollector->__construct() (line 114 of core/lib/Drupal/Core/Cache/CacheCollector.php).
Drupal\Core\Cache\CacheCollector->__construct('state', Object, Object) (Line: 33)
Drupal\Core\State\State->__construct(Object, Object, Object) (Line: 276)
Drupal\Component\DependencyInjection\Container->createService(Array, 'state') (Line: 177)
Drupal\Component\DependencyInjection\Container->get('state', 1) (Line: 494)
Drupal\Component\DependencyInjection\Container->resolveServicesAndParameters(Array) (Line: 236)
...
Deprecated function: assert(): Calling assert() with a string argument is deprecated in Drupal\Core\Plugin\DefaultPluginManager->setCacheBackend() (line 151 of core/lib/Drupal/Core/Plugin/DefaultPluginManager.php).
Drupal\Core\Plugin\DefaultPluginManager->setCacheBackend(Object, 'entity_type', Array) (Line: 79)
Drupal\Core\Entity\EntityTypeManager->__construct(Object, Object, Object, Object, Object) (Line: 284)
Drupal\Component\DependencyInjection\Container->createService(Array, 'entity_type.manager') (Line: 177)
Drupal\Component\DependencyInjection\Container->get('entity_type.manager', 1) (Line: 494)
...
Deprecated function: assert(): Calling assert() with a string argument is deprecated in Drupal\Core\Cache\Cache::mergeTags() (line 57 of core/lib/Drupal/Core/Cache/Cache.php).
Drupal\Core\Cache\Cache::mergeTags(Array, Array) (Line: 265)
Drupal\Core\Config\ConfigBase->getCacheTags() (Line: 172)
Drupal\Core\Cache\CacheableMetadata::createFromObject(Object) (Line: 210)
Drupal\Core\Config\Entity\ConfigEntityStorage->doLoadMultiple(NULL) (Line: 242)
...
Deprecated function: assert(): Calling assert() with a string argument is deprecated in Drupal\Core\Access\AccessResult::neutral() (line 42 of core/lib/Drupal/Core/Access/AccessResult.php).
Drupal\Core\Access\AccessResult::neutral() (Line: 130)
Drupal\Core\Access\AccessManager->check(Object, Object, Object, 1) (Line: 112)
Drupal\Core\Access\AccessManager->checkRequest(Object, Object, 1) (Line: 107)
Drupal\Core\Routing\AccessAwareRouter->checkAccess(Object) (Line: 92)
Drupal\Core\Routing\AccessAwareRouter->matchRequest(Object) (Line: 154)

It works fine in PHP 7.1