&required=`field picker...`
[[!getUrlParam? &name=`key`]]
This question has been answered by BobRay. See the first response.
The exception is if it is not an optional field in which case everything works perfectly.

[[!getUrlParam? &name=`key`]]
[[+caption]]
<dd title="Filter by ‘Time’"> Completion Time: [[!toLinks? &items=`[[*time]]` &target=`22` &tpl=`Specs Link` &tagKey=`time` ]] </dd>
[[ShowCaption? &name=`[[+name]]` ]]
<?php
/* ShowCaption snippet */
$output = '';
$name = $modx->getOption('name', $scriptProperties, '', true);
if (!empty($name)) {
$tv = $modx->getObject('modTemplateVar', array('name' => $name));
if ($tv) {
$output = $tv->get('caption');
}
}
return $output;
[[%mn.[[+name]]? &namespace=`mynamespace` &topic=`default` &language=`en`]]
<a href="[[+url]]">[[+item]]</a>
[[!ShowCaption? &name=`[[+name]]` ]]
[[!ShowCaption? &name=`[[!getUrlParam? &name=`key`]]`]]
<?php
/* ShowCaption snippet */
$output = 'No Caption';
$name = $modx->getOption('name', $scriptProperties, '', true);
if (!empty($name)) {
$tv = $modx->getObject('modTemplateVar', array('name' => $name));
if ($tv) {
$output = $tv->get('caption');
}
}
return $output;[[!ShowCaption]]
<?php
/* ShowCaption snippet */
$output = 'No Caption';
$fields = array('name' => 'key');
$name = $modx->runSnippet('getUrlParam', $fields);
if (!empty($name)) {
$tv = $modx->getObject('modTemplateVar', array('name' => $name));
if ($tv) {
$output = $tv->get('caption');
}
}
return $output;