Properties on union schema?

[Christophe Taton]

Hi,
I'm toying with a few changes to provide alternative representations of
union fields in Java (somewhat related to
https://issues.apache.org/jira/browse/AVRO-248).
To experiment with this, I'd like to set properties on union schemas, but
properties are currently disabled on unions.
Is there a particular reason for this, or is it a reasonable change to
allow properties on unions?
Thanks,
C.