If Data.pm is your file, I'd clarify first if $data is really not initialized.

NB: it's possible (and easily implemented) that a module delegates the warning line and file to the caller, probably that's what XML::Simple is doing. *

update

*) At least it's using Carp

˛) from warnings : This means that the scope of the warning pragma is limited to the enclosing block. It also means that the pragma setting will not leak across files (via use, require or do). This allows authors to independently define the degree of warning checks that will be applied to their module. (emphasis added)

Have you determined which of the values it is complaining about (is it maybe RootName => undef, or $data as LanX pointed out)? Have you tried any alternatives, i.e. making sure you're not feeding the function undefs where you shouldn't be? Note the effect of warnings is lexical in scope, so it won't change anything coming from inside of XML::Simple. If that is the case, and you're feeding the function valid data, you could try the following ugly hack to suppress all warnings from inside XMLout (although it's about as ugly as using XML::Simple for XML output in the first place...): my $xmlout = do { local $SIG{__WARN__}=sub{}; XMLout(...) };

Minor edits for clarification.

It looks like $data is undefined.

#!/bin/env perl
use strict;
use warnings;
use XML::Simple;

# From https://metacpan.org/pod/XML::Simple#QUICK-START
my $data =   {
    'logdir'        => '/var/log/foo/',
    'debugfile'     => '/tmp/foo.debug',
    'server'        => {
        'sahara'        => {
            'osversion'     => '2.6',
            'osname'        => 'solaris',
            'address'       => [ '10.0.0.101', '10.0.1.101' ]
        },
        'gobi'          => {
            'osversion'     => '6.5',
            'osname'        => 'irix',
            'address'       => [ '10.0.0.102' ]
        },
        'kalahari'      => {
            'osversion'     => '2.0.34',
            'osname'        => 'linux',
            'address'       => [ '10.0.0.103', '10.0.1.103' ]
        }
    }
};

print "XMLout with data defined:\n\n", xml_out($data), "\n\n";
#print "XMLout with data undefined:\n\n", xml_out(undef), "\n\n";

sub xml_out {
  my $data = shift;
  my $xmlout = XMLout($data, NoAttr => 1, RootName => undef, SuppressE
+mpty => 0);
  return '<xml version="1.0" encoding="UTF-8">' . "\n$xmlout</xml>";
}
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Running this produces no warning but if you uncomment the second print it does.

Thank you for the replies.

I'm not sure I realized that "no warnings" wouldn't affect warnings emitted by XML::Simple. I think I knew this in the back of my head, but I added that at some point and it must have worked--perhaps accidentally, combined with some other change--so I never considered it.

I also don't know why the warnings re-started recently.

In any case, I'm absolutely sure that $data itself was defined.

However, after a bunch more testing, I realized that I was getting these warnings for any undefined values in the data. And then I realized that the error was that SuppressEmpty => 0 was a mistake--it's supposed to be SuppressEmpty => undef (or the empty string). When I made this change, the warnings went away, and I got my desired empty XML in the output.

I have no idea why it (seemed to) work at one point and then go back to not working. However, it's clear that the SuppressEmpty setting was the right way to fix it.

Thanks again.

Hmm, it looks weird that a boolean switch should accept 1 but not 0. (???)

So I took a look into the documentation. ...

Turns out that  SuppressEmpty is not a real flag, but that "" and undef are used to define how empty elements are represented or ignored in a case of a true value.

And the docs explicitly talk about "suppressing the generation of warnings" in XMLout().

I find the naming and concept too error prone.

Something like  RepresentEmpty => "off" | "" | undef might have been a better choice.

And I'm understanding even better now, why this module is discouraged, even in its own POD.

Cheers Rolf
_{(addicted to the Perl Programming Language and ☆☆☆☆ :)
Je suis Charlie!}