diff --unified --recursive --text gnuradio-3.8.2.0.orig/grc/gui/ParamWidgets.py gnuradio-3.8.2.0/grc/gui/ParamWidgets.py
--- gnuradio-3.8.2.0.orig/grc/gui/ParamWidgets.py	2021-06-11 09:50:18.588097897 +0300
+++ gnuradio-3.8.2.0/grc/gui/ParamWidgets.py	2021-06-11 09:52:57.974027799 +0300
@@ -35,7 +35,7 @@
         """
         Check if a theme is dark based on its name.
         """
-        return theme_name in Constants.GTK_DARK_THEMES or "dark" in theme_name.lower()
+        return theme_name and (theme_name in Constants.GTK_DARK_THEMES or "dark" in theme_name.lower())
     # GoGoGo
     config = configparser.ConfigParser()
     config.read(os.path.expanduser(Constants.GTK_SETTINGS_INI_PATH))