code: public void setFields(Map<String, String> fields) {
          _fields.clear();
          if (fields != null) {
              _fields.putAll(fields);
          }
      }
docs: Replaces the user defined fields associated with the annotation. This information can be used to store information about the annotation such as
  the event name, the associated user or any other relevant information. Existing fields will always be deleted.
  
  @param  fields  The user defined fields. May be null.