Additional fix to #4728.

framework/filters/HttpCache.php

@@ -152,9 +152,9 @@ class HttpCache extends ActionFilter
         if (isset($_SERVER['HTTP_IF_NONE_MATCH'])) {
             // HTTP_IF_NONE_MATCH takes precedence over HTTP_IF_MODIFIED_SINCE
             // http://tools.ietf.org/html/rfc7232#section-3.3
-            return $etag === null || in_array($etag, Yii::$app->request->getEtags(), true);
+            return $etag !== null && in_array($etag, Yii::$app->request->getEtags(), true);
         } elseif (isset($_SERVER['HTTP_IF_MODIFIED_SINCE'])) {
-            return $lastModified === null || @strtotime($_SERVER['HTTP_IF_MODIFIED_SINCE']) >= $lastModified;
+            return $lastModified !== null && @strtotime($_SERVER['HTTP_IF_MODIFIED_SINCE']) >= $lastModified;
         } else {
             return $etag === null && $lastModified === null;
         }

tests/unit/framework/filters/HttpCacheTest.php

@@ -51,7 +51,7 @@ class HttpCacheTest extends \yiiunit\TestCase
         $this->assertFalse($method->invoke($httpCache, 0, '"foos"'));
         $this->assertTrue($method->invoke($httpCache, 1, '"foo"'));
         $this->assertFalse($method->invoke($httpCache, 1, '"foos"'));
-        $this->assertTrue($method->invoke($httpCache, null, null));
+        $this->assertFalse($method->invoke($httpCache, null, null));
     }
 
     /**