指北针符号是什么类型，转换成ISymbol类型为null

IEnumStyleGalleryItem pEnumStyleGalleryItem = pStyleGallery.Items[“North Arrows”, "", ""];
IStyleGalleryItem pStyleGalleryItem = null;
while ((pStyleGalleryItem = pEnumStyleGalleryItem.Next()) != null)
{
var symbol= pStyleGalleryItem.Item as ISymbol;//类型转换后符号为null
}