Why is the character set for the uca1400_ai_ci collation NULL?

I've been working with database collations of late. I generally don't like ambiguous queries such as SHOW COLLATION so I eventually found the source via the following query: SELECT * FROM information_schema.COLLATIONS ORDER BY CHARACTER_SET_NAME ASC, COLLATION_NAME ASC; I now have the option to update the collation to uca1400_ai_ci however the associated character set value is NULL. Why is the uca1400_ai_ci NULL and what, if any considerations should I have while updating from the character set utf8mb4 and collation utf8mb4_unicode_520_ci?