Binding undefs in DBD::Oracle

[Paul G. Weiss]

I always that the binding undef's in DBD::Oracle was the way to bind a  
null, yet:

  DB<5> x $dbh->selectall_arrayref('select x,b from tbl where a=?', undef,  
4)
0  ARRAY(0x9b53010)
   0  ARRAY(0x9ba6284)
      0  'bbc0dfec7ba578f2dafc8f2eb42fbd3ae17cf300'
      1  undef

but

  DB<3> x $dbh->selectall_arrayref('select x,b from tbl where a=? and  
b=?', undef, 4, undef)
0  ARRAY(0x9ba0530)
     empty array

i.e. the 'b=?' in the statement where I bind the value to undef does _not_  
act like
'b is null'.

Didn't this used to work?  I've tried this with DBD::Oracle v1.16 and 1.17.

-P