Handle the case where currentLanguage is null.

[maliming]

Default Language may not be in the language list.

abp/framework/src/Volo.Abp.AspNetCore/Microsoft/AspNetCore/RequestLocalization/DefaultAbpRequestLocalizationOptionsProvider.cs

Lines 89 to 99 in 1a622bc

	private static RequestCulture DefaultGetRequestCulture(string defaultLanguage, IReadOnlyList<LanguageInfo> languages)
	{
	if (defaultLanguage == null)
	{
	var firstLanguage = languages.First();
	return new RequestCulture(firstLanguage.CultureName, firstLanguage.UiCultureName);
	}
	var (cultureName, uiCultureName) = LocalizationSettingHelper.ParseLanguageSetting(defaultLanguage);
	return new RequestCulture(cultureName, uiCultureName);
	}