Blockbase: Remove the fallback for the navigation block (#5419)

blockbase/functions.php

@@ -174,6 +174,14 @@ add_action(
 	}
 );
 
+/**
+ * Disable the fallback for the core/navigation block.
+ */
+function blockbase_core_navigation_render_fallback() {
+	return null;
+}
+add_filter( 'block_core_navigation_render_fallback', 'blockbase_core_navigation_render_fallback' );
+
 /**
  * Block Styles.
  */