In the custom template for lot details, settings>system parameters>custom templates, under lot item detail page, there might be a placeholder for a custom field eg. {custom_field}. When you review the page source for a lot details page, you will notice an empty link rendered eg. view-source: lot-details/index/catalog/25265/lot/3726927.
Since this is what the search engine crawlers are following, it is best to use BEGIN-END block decoration eg.--{custom_field_begin}{custom_field}{custom_field_end} -- to avoid rendering anything for specific empty fields.