Parsing XML documents with Perl's XML::Simple

Thank you for this excellent article. I am having a specific problem accessing the content of the reference fields in a xml::simple parsed xml file and I hope someone can help.
Specifically, there are records in the xml document that have no reference, some that have one, and some that have more than one. How do I capture
the values of the references (ie. content) in an array if the values exist, and avoid a program termination if it does not exist? Thank you in advance for the help.

Here is the perl code fragment, it retrieves the category and text values very easily. I am having difficulty
with the @annotationreferencekey variable:

#!C:\perl\bin
use XML::Simple;

@annotationkeyarray = qw(AN000036741 AN000036745 AN000036743 AN000036744);
#AN000036744 no item value, AN000036743 has two items

my $treeparser = new XML::Simple(ForceArray => 1);
my $annotationtree = $treeparser->XMLin("annotate_example.xml");

foreach $annotationkey (@annotationkeyarray){
$annotationcategory = $annotationtree->{Annotate}->{"$annotationkey"}->{category}->[0];
$annotationtext = $annotationtree->{Annotate}->{"$annotationkey"}->{text}->[0];
@annotationreferencekey = $annotationtree->{Annotate}->{"$annotationkey"}->{source}->{item}->{content}->[0];
print "$annotationkey:$annotationcategory:$annotationtext:@annotationreferencekey\n";
}

The actual xml file (annotate_example.xml) is:

category 1
one reference instance 1

23058

category 2
two references

23058
23099

category 3
no references

category 4
one reference instance 2

23055

The output from data::dumper is:

$VAR1 = {
'source' => 'bbdb82',
'Annotate' => {
'AN000036743' => {
'source' => [
{
'item' => [
{
'xlink:show' => 'new',
'xlink:actuate' => 'onRequest',
'xlink:href' => 'reference.xml#ID (TFPA23058)',
'content' => '23058',
'type' => 'Reference',
'xlink:type' => 'simple'
},
{
'xlink:show' => 'new',
'xlink:actuate' => 'onRequest',
'xlink:href' => 'reference.xml#ID (TFPA23099)',
'content' => '23099',
'type' => 'Reference',
'xlink:type' => 'simple'
}
]
}
],
'text' => [
'two references'
],
'category' => [
'category 2'
]
},
'AN000036744' => {
'source' => [
{}
],
'text' => [
'no references'
],
'category' => [
'category 3'
]
},
'AN000036741' => {
'source' => [
{
'item' => [
{
'xlink:show' => 'new',
'xlink:actuate' => 'onRequest',
'xlink:href' => 'reference.xml#ID (TFPA23058)',
'content' => '23058',
'type' => 'Reference',
'xlink:type' => 'simple'
}
]
}
],
'text' => [
'one reference instance 1'
],
'category' => [
'category 1'
]
},
'AN000036745' => {
'source' => [
{
'item' => [
{
'xlink:show' => 'new',
'xlink:actuate' => 'onRequest',
'xlink:href' => 'reference.xml#ID (TFPA23055)',
'content' => '23055',
'type' => 'Reference',
'xlink:type' => 'simple'
}
]
}
],
'text' => [
'one reference instance 2'
],
'category' => [
'category 4'
]
}
},
'version' => '5.2',
'xmlns:xlink' => 'http://www.w3.org/1999/xlink',
'extent' => 'annotate'
};