MAGETWO-50551: When saving product or category cache cleared by general tag

- Code cleanup.

Author: Hayder Sharhan

app/code/Magento/CacheInvalidate/Observer/InvalidateVarnishObserver.php

@@ -50,7 +50,9 @@ public function execute(\Magento\Framework\Event\Observer $observer)
                 foreach ($object->getIdentities() as $tag) {
                     $tags[] = sprintf($pattern, $tag);
                 }
-                $this->purgeCache->sendPurgeRequest(implode('|', array_unique($tags)));
+                if (!empty($tags)) {
+                    $this->purgeCache->sendPurgeRequest(implode('|', array_unique($tags)));
+                }
             }
         }
     }

app/code/Magento/Catalog/Model/Product.php

@@ -2268,7 +2268,7 @@ public function getIdentities()
                 $identities[] = self::CACHE_PRODUCT_CATEGORY_TAG . '_' . $categoryId;
             }
         }
-        if ($this->getAppState()->getAreaCode() === 'frontend') {
+        if ($this->getAppState()->getAreaCode() === \Magento\Framework\App\Area::AREA_FRONTEND) {
             $identities[] = self::CACHE_TAG;
         }
         return array_unique($identities);
@@ -2560,27 +2560,16 @@ public function setId($value)
     /**
      * Get application state
      *
+     * @deprecated
      * @return \Magento\Framework\App\State
      */
     private function getAppState()
     {
         if (!$this->appState instanceof \Magento\Framework\App\State) {
-            return \Magento\Framework\App\ObjectManager::getInstance()->get('Magento\Framework\App\State');
-        } else {
-            return $this->appState;
+            $this->appState = \Magento\Framework\App\ObjectManager::getInstance()->get(
+                \Magento\Framework\App\State::class
+            );
         }
-    }
-
-    /**
-     * Set application state
-     *
-     * @deprecated
-     * @param \Magento\Framework\App\State $appState
-     * @return $this
-     */
-    public function setAppState(\Magento\Framework\App\State $appState)
-    {
-        $this->appState = $appState;
-        return $this;
+        return $this->appState;
     }
 }