fix whoops being instantiated when not available

Author: atanas-dev

src/Exceptions/ExceptionsServiceProvider.php

@@ -26,6 +26,10 @@ public function register( $container ) {
 		] );
 
 		$container['whoops'] = function( $container ) {
+			if ( ! class_exists( Run::class ) ) {
+				return null;
+			}
+
 			$run = new Run();
 			$run->allowQuit( false );
 			$run->pushHandler( new PrettyPageHandler() );