Catch exception caused by missing widget parent.

src/napari_mm3/_deriving_widgets.py

@@ -443,7 +443,11 @@ def _save_settings(self):
         name == 'widget_name'.
         Apply the saved parameters to the currently extant widgets.
         """
-        widget_name = self.parent.name
+        try:
+            widget_name = self.parent.name
+        except:
+            warning('Could not extract widget name to save settings.')
+            widget_name = ''
         history = []
         if Path("./history.json").exists():
             with open("./history.json", "r") as h:
@@ -469,6 +473,7 @@ def _save_settings(self):
             json.dump(history, h, indent=2)
 
 
+
 class TimeRangeSelector(RangeEdit):
     def __init__(self, permitted_times):
         label_str = f"time range (frames {permitted_times[0]}-{permitted_times[1]})"