Add docs

core/generator/generator_container.gd

@@ -147,7 +147,14 @@ func _refresh_buff_rows(can_interact: bool) -> void:
 		row.tile.set_runtime(level, effect_text, cost_text, can_buy, false)
 	
 func _refresh_generator_ui() -> void:
+	if _buy_button == null or _buy_max_button == null:
+		return
+	
+	if _generator == null:
+		return
+	
 	var can_interact: bool = _generator.is_available_to_player()
+	
 	_buy_button.disabled = not can_interact
 	_buy_max_button.disabled = not can_interact