system: FileReference.nodes fix when reference contains no nodes
system: FileReference.nodes fix when reference contains no nodes

assumptionsoup/pymel,leonsooi/pymel,shrtcww/pymel,juggernate/pymel,david-lassonde-adsk/pymel,david-lassonde-adsk/pymel,AtonLerin/pymel,juggernate/pymel,assumptionsoup/pymel,AtonLerin/pymel,leonsooi/pymel,shrtcww/pymel