Use of "defined" on aggregates (hashes and arrays) is depre-
  cated.  It used to report whether memory for that aggregate has
  ever been allocated.  This behavior may disappear in future
  versions of Perl.  You should instead use a simple test for
  size:

        if (@an_array) { print "has array elements\n" }
        if (%a_hash)   { print "has hash members\n"   }