core/modules/block/src/BlockViewBuilder.php | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/core/modules/block/src/BlockViewBuilder.php b/core/modules/block/src/BlockViewBuilder.php
index f674d68..089be8a 100644
--- a/core/modules/block/src/BlockViewBuilder.php
+++ b/core/modules/block/src/BlockViewBuilder.php
@@ -105,7 +105,7 @@ public function buildBlock($build) {
     // Remove the block entity from the render array, to ensure that blocks
     // can be rendered without the block config entity.
     unset($build['#block']);
-    if (!Element::isEmpty($content)) {
+    if ($content !== NULL && !Element::isEmpty($content)) {
       // Place the $content returned by the block plugin into a 'content' child
       // element, as a way to allow the plugin to have complete control of its
       // properties and rendering (e.g., its own #theme) without conflicting