hugo/docs/content/en/functions/collections/IsSet.md

title	description	categories	keywords	action	aliases
collections.IsSet	Reports whether the key exists within the collection.			aliases related returnType signatures isset functions/collections/Dictionary functions/collections/Group functions/collections/IndexFunction functions/collections/Where functions/go-template/if functions/go-template/with bool collections.IsSet COLLECTION KEY	/functions/isset

For example, consider this site configuration:

{{< code-toggle file=hugo >}} [params] showHeroImage = false {{< /code-toggle >}}

It the value of showHeroImage is true, we can detect that it exists using either if or with:

{{ if site.Params.showHeroImage }}
  {{ site.Params.showHeroImage }} → true
{{ end }}

{{ with site.Params.showHeroImage }}
  {{ . }} → true
{{ end }}

But if the value of showHeroImage is false, we can't use either if or with to detect its existence. In this case, you must use the isset function:

{{ if isset site.Params "showheroimage" }}
  <p>The showHeroImage parameter is set to {{ site.Params.showHeroImage }}.<p>
{{ end }}

{{% note %}} When using the isset function you must reference the key using lower case. See the previous example. {{% /note %}}