In the Systems Reference Document (SRD) text of polymorph it is stated that
The spell has no effect on a shapechanger or a creature with 0 hitpoints
However in my PHB copy it is worded as
An unwilling creature must make a Wisdom saving throw to avoid the effect. A shapechanger automatically succeeds on this saving throw.
Implying that a willing shapechanger can be effected since it only allows a success on a save that is only rolled by an unwilling target. I was unable to find an errata on this subject.
What is the RAW in this case? The SRD was published later than PHB--does it make it more official? Is this even an intentional change? Is there an errata I am missing somewhere?