Spring The Bug of DeferredImportSelectorHandler !

Dear Spring Boot Team: I think the handle method has a bug , the deferredImportSelectors can not be null forever ! My version is 2.3.3.RELEASE .

private class DeferredImportSelectorHandler {

    @Nullable
    private List<DeferredImportSelectorHolder> deferredImportSelectors = new ArrayList<>();

    public void handle(ConfigurationClass configClass, DeferredImportSelector importSelector) {
        DeferredImportSelectorHolder holder = new DeferredImportSelectorHolder(configClass, importSelector);
        // This can not be null forever !
        if (this.deferredImportSelectors == null) {
            DeferredImportSelectorGroupingHandler handler = new DeferredImportSelectorGroupingHandler();
            handler.register(holder);
            handler.processGroupImports();
        }else {
            this.deferredImportSelectors.add(holder);
        }
    }
}