Merge pull request #686 from gszy/cache-options-instance

The Options\Cache::instance property can be null

src/DoctrineModule/Options/Cache.php

@@ -38,7 +38,7 @@ class Cache extends AbstractOptions
  * Key to use for fetching the memcache, memcached, or redis instance from
  * the service locator. Used only with Memcache. Memcached, and Redis.
  *
- * @var string
+ * @var null|string
  */
  protected $instance = null;
 
@@ -61,9 +61,9 @@ public function setInstance(string $instance) : self
  return $this;
  }
 
- public function getInstance() : string
+ public function getInstance() : ?string
  {
- return (string) $this->instance;
+ return $this->instance;
  }
 
  public function setNamespace(string $namespace) : self