fix test failure

jdaviz/configs/specviz/plugins/unit_conversion/unit_conversion.py

@@ -244,7 +244,7 @@ def _on_add_data_to_viewer(self, msg):
                 # data already existed in this viewer and display units were already set
                 return
 
-            # this spectral viewer was empty (did not have display units set yet),
+            # this spectral viewer was empty (did not have display units set yet),˜
             # but global selections are available in the plugin,
             # so we'll set them to the viewer here
             viewer.state.x_display_unit = self.spectral_unit_selected
@@ -346,7 +346,8 @@ def _handle_attribute_display_unit(self, attr_unit, layers=None):
             # DQ layer doesn't play nicely with this attribute
             if "DQ" in layer.layer.label or isinstance(layer.layer, GroupedSubset):
                 continue
-            elif u.Unit(layer.layer.get_component("flux").units).physical_type != 'surface brightness':  # noqa
+            elif ("flux" in [str(c) for c in layer.layer.components]
+                    and u.Unit(layer.layer.get_component("flux").units).physical_type != 'surface brightness'):  # noqa
                 continue
             if hasattr(layer, 'attribute_display_unit'):
                 layer.attribute_display_unit = attr_unit