You've been the victim of auto-vivification:

use strict;
use warnings;

my $arrayref;

foreach (@$arrayref) {
}

print($arrayref\n");  # ARRAY(0x1abefc0)
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scalar @$arrayref doesn't autovivify, therefore if (@$arrayref) { ... } gives an error.

---

If you don't distiguish between undefined and 0 elements, you could create a 0-element array when the function returns undef:

use strict;
use warnings;

my $arrayref = getArrayref(); # this sometimes returned undef

# Manually vivify it.
$arrayref ||= [];

if (@$arrayref) {
   ...
}
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Otherwise, yes, you have to check if it's defined (or simply true) first:

use strict;
use warnings;

my $arrayref = getArrayref(); # this sometimes returned undef

if ($arrayref && @$arrayref) {
   ...
}
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