I use small subs for this: 
sub undef2blank
{
  return defined($_[0]) ? $_[0] : "";
}

my $outPath = $obj->{outpath}{absolut} . "-" . undef2blank($obj->{sap}
+{jfExtNum});

[download]
It's probaby slower than the other ideas suggested here, but it's obvious what it does and keeps the general style of the original code.

In reply to Re: concatenating partially uninitialized values by sgifford
in thread concatenating partially uninitialized values by tos

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