Can NULL RRs still be used or should be generally avoided?

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http://serverfault.com – I'm searching for a way for a placeholder in my bind zone files. I found some information on the NULL RR which would be perfect, but wikipedia states it's obsolete by RFC 883. I read through this RFC but could not find any reference for this statement. Is the NULL RR obsolete or not? Is it acceptable to use it as placeholder? At the moment I use this: somename IN TXT "placeholder" (HowTos)