code: @InterfaceAudience.Public
      public Map<String, Object> getProperties() {
          return getCurrentRevision() == null ? null : getCurrentRevision().getProperties();
      }
docs: The contents of the current revision of the document.
  This is shorthand for self.currentRevision.properties.
  Any keys in the dictionary that begin with "_",
  such as "_id" and "_rev", contain CouchbaseLite metadata.
  
  @return contents of the current revision of the document.
  null if currentRevision is null