anchor.diff:      [
           #triple{
               predicate = rdf_property:schema(<<"startDate">>),
  -            object = #rdf_value{value = Value}
  +            object = #rdf_value{value = z_datetime:undefined_if_invalid_date(Value)}
           }
       ];
   property_to_triples({date_end, Value}, _Properties, _Context) ->
       [
           #triple{
               predicate = rdf_property:schema(<<"endDate">>),
  -            object = #rdf_value{value = Value}
  +            object = #rdf_value{value = z_datetime:undefined_if_invalid_date(Value)}
           }
       ];
   property_to_triples({license, Value}, _Properties, _Context) ->
  
positive.code:                 }
              ]
      end;
  
  edge_to_triples(_Edge, _Uri, _Subject, _Object, _Context) ->
      %% Ignore all other edges.
  
negative.code:         }
      ];
  property_to_triples({body, Value}, _Properties, Context) ->
      m_rdf_export:translations_to_rdf(rdf_property:schema(<<"text">>), Value, Context);
  property_to_triples({created, Value}, _Properties, _Context) ->
      [
          #triple{
  