fix subset histogram update bug in plot options (spacetelescope#2393)

CHANGES.rst

@@ -95,6 +95,9 @@ Bug Fixes
   the selection when the choices change if any of the previous entries are still
   valid. [#2344]
 
+- Fixed Plot Options stretch histogram bug that raised an error when a spatial subset
+  was selected in Imviz and Cubeviz. [#2393]
+
 Cubeviz
 ^^^^^^^
 

jdaviz/configs/default/plugins/plot_options/plot_options.py

@@ -4,6 +4,7 @@
 from astropy.visualization import PercentileInterval
 from traitlets import Any, Dict, Float, Bool, Int, List, Unicode, observe
 
+from glue.core.subset_group import GroupedSubset
 from glue.viewers.scatter.state import ScatterViewerState
 from glue.viewers.profile.state import ProfileViewerState, ProfileLayerState
 from glue.viewers.image.state import ImageSubsetLayerState
@@ -579,6 +580,10 @@ def _update_stretch_histogram(self, msg={}):
             # skip further updates if no data are available:
             return
 
+        if isinstance(data, GroupedSubset):
+            # don't update histogram for subsets:
+            return
+
         comp = data.get_component(data.main_components[0])
 
         # TODO: further optimization could be done by caching sub_data