LeadConversionWizard::prepareDataForSave

public function prepareDataForSave($entityTypeID, array &$fields)
{
	$dstUserFields = LeadConversionMapper::getUserFields($entityTypeID);
	foreach($dstUserFields as $dstName => $dstField)
	{
		if($dstField['USER_TYPE_ID'] === 'file')
		{
			$this->prepareFileUserFieldForSave($dstName, $dstField, $fields);
		}
	}

	/** @var LeadConverter $converter */
	$converter = $this->converter;
	$mappedFields = $converter->mapEntityFields($entityTypeID, array('DISABLE_USER_FIELD_INIT' => true));
	if(!empty($mappedFields))
	{
		$merger = EntityMerger::create($entityTypeID, $converter->getUserID(), true);

		//Skip empty fields if user has left theirs empty.
		$merger->mergeFields(
			$mappedFields,
			$fields,
			true,
			[
				'ENABLE_UPLOAD' => true,
				'SKIP_MULTIPLE_USER_FIELDS' => $this->isSkipMultipleUserFields(),
			]
		);
	}
}