Hi, often you can skip a `defined` check to decide whether or not you can dereference something, without autovivifying it if it doesn't exist, by supplying a default. Note use of the defined-or operator //.

$ perl -MData::Dumper -Mstrict -wE 'my $foo = {}; say for @{ $foo->{ba
+r} }; say Dumper $foo'
$VAR1 = {
          'bar' => []
        };
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$ perl -MData::Dumper -Mstrict -wE 'my $foo = {}; say for @{ $foo->{ba
+r} // [] }; say Dumper $foo'
$VAR1 = {};
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This should work if I understand your partial code sample:

    open(my $fh, '<', "$file_path") or return 0;

    my $href = {};

    while (my $line = <$fh>) {
    
        # ...........
        # ...........
        # Additional operations of the lines of the file
        # ...........
        # ...........
        
        push @{ $href->{test} }, {
            group  => $group,
            values => [ sort uniq $value, @{ $href->{values} // [] } ]
+,
        };
    }
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(...although it seems a bit odd to have a top-level key with values that are then added to the sub-hashes. Could you build the combined list when you use the contents of $href?)

Hope this helps!