favicon property
Favicon is a 64px icon URL derived from the host for the client to render beside the citation. It is Google's s2 service, not something we host or fetched — an empty host yields the empty string.
Please note: This property should have been non-nullable! Since the specification file does not include a default value (using the "default:" property), however, the generated source code must fall back to having a nullable type. Consider adding a "default:" property in the specification file to hide this note.
Implementation
String? favicon;