def predicate
      if instance_variable_defined?(:@predicate)
        @predicate
      else
        rdf_node = Redland.librdf_statement_get_predicate(rdf_statement)
        @predicate = rdf_node.null? ? nil : Node.new(rdf_node)
      end
    end
def predicate
      if instance_variable_defined?(:@predicate)
        @predicate
      else
        rdf_node = Redland.librdf_statement_get_predicate(rdf_statement)
        @predicate = rdf_node.null? ? nil : Node.new(rdf_node)
      end
    end
Predicate of the statement.

 @return [Node, nil]