I tend to generate the sitemaps for my static sites (no CMS) by using a service such as xml-sitemaps.com. They way this works if you input your homepage and it crawls all the internal links of a site and then generates you a .xml file. The problem with this is because its crawling from the homepage if a page if not linked to i.e. a 404 page it won't be included in the sitemap.Is it good practice to have the 404 page in there?
Should 404 pages feature in your sitemap.xml
sitemap;404
Sitemap.xml helps your website to be well and fast indexed. By submitting this file to search engines, I don't see any good reason to ask them to index a page that doesn't exist (404 HTTP status).