HistoryMetadata constructor
      
      HistoryMetadata({ 
    
    
- String? activityDescription,
- String? activityDescriptionKey,
- HistoryMetadataParticipant? actor,
- HistoryMetadataParticipant? cause,
- String? description,
- String? descriptionKey,
- String? emailDescription,
- String? emailDescriptionKey,
- Map<String, dynamic> ? extraData,
- HistoryMetadataParticipant? generator,
- String? type,
Implementation
HistoryMetadata(
    {this.activityDescription,
    this.activityDescriptionKey,
    this.actor,
    this.cause,
    this.description,
    this.descriptionKey,
    this.emailDescription,
    this.emailDescriptionKey,
    this.extraData,
    this.generator,
    this.type});