Add check if subset label not in dc subset groups

jdaviz/app.py

@@ -915,7 +915,14 @@ def get_subsets(self, subset_name=None, spectral_only=False,
                     all_subsets[label] = [reg['region'] for reg in subset_region]
                 else:
                     all_subsets[label] = subset_region
-        return all_subsets[subset_name] if subset_name else all_subsets
+
+        all_subset_names = [subset.label for subset in dc.subset_groups]
+        if subset_name and subset_name in all_subset_names:
+            return all_subsets[subset_name]
+        elif subset_name:
+            raise ValueError(f"{subset_name} not in {all_subset_names}")
+        else:
+            return all_subsets
 
     def _remove_duplicate_bounds(self, spec_regions):
         regions_no_dups = None