Allow specifying NULL default in pg_proc.dat for "any" arguments

I noticed a small gap in our recent addition of default arguments for 
functions in pg_proc.dat - it chokes if you try to set the default for a 
VARIADIC "any" argument. But there's no need if the default argument us 
NULL, as it often is. We don't need the argument's type_io_data etc. in 
such a case. So this patch just handles NULL without fetching any type info.


cheers


andrew

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Andrew Dunstan
EDB: https://www.enterprisedb.com