The cornmeal called for is really only necessary if you are using canned beans. Canned beans tend to be a bit water logged and will make a stickier hamburger patty because of the excess liquid they hold. If you are using cooked black beans from dry beans, you shouldn't need to use it because they are not as wet as the canned variety and make an easy to work with paste.
* To cook black beans from dried bean, rinse 3 cups of dry black beans in a sieve under cold water. Place beans in a stock pot and cover with three times as much water as there are beans. Bring to a boil and let boil for 2 minutes. Turn the heat off and cover with a lid. Let the pot of beans soak for 2 hours. Drain the water and add fresh water back in(about twice as much as there are beans). Bring to a simmer and cover, cooking on medium heat, until the beans are tender, about 1 hour. Do not add salt, this could cause the beans to toughen. Drain the beans and use according to the recipe. This will make a little over 6 cups of cooked beans.