#1 Make sure arguments are configured before setting them.

src/Plugin/views/display/ViewsBvbBlock.php

@@ -287,7 +287,7 @@ class ViewsBvbBlock extends Block {
     }
 
     // Save arguments.
-    $args = $form_state->getValue('override')['arguments'];
+    $args = $form_state->getValue('override')['arguments'] ?? [];
     $form_state->unsetValue(['override', 'arguments']);
     $block->setConfigurationValue('arguments', $args);
   }