If no spaces, prompt the user to create one

src/SpaceListBuilder.php

@@ -53,13 +53,31 @@ class SpaceListBuilder extends EntityListBuilder {
    * {@inheritdoc}
    */
   public function render() {
-    $build['table'] = parent::render();
+    $build = parent::render();
+
+    $build['table']['#empty'] = $this->t(
+      "No spaces available, please <a href='@link'>create a new space.</a>",
+      [
+        '@link' => Url::fromUserInput('/space/add')->toString(),
+      ]
+    );
 
     $total = $this->getStorage()
       ->getQuery()
       ->accessCheck(FALSE)
       ->count()
-      ->execute();
+    ->execute();
+
+    if (!$total) {
+      $this->messenger()->addWarning(
+        $this->t(
+          "No spaces available, please <a href='@link'>create a new space.</a>",
+          [
+            '@link' => Url::fromUserInput('/space/add')->toString(),
+          ]
+        )
+      );
+    }
 
     $build['summary']['#markup'] = $this->t('Total spaces: @total', ['@total' => $total]);
     $build['summary']['#weight'] = 0;