diff --git a/Orange/widgets/gui.py b/Orange/widgets/gui.py
index 75b45896586..ebae96e3acf 100644
--- a/Orange/widgets/gui.py
+++ b/Orange/widgets/gui.py
@@ -503,14 +503,14 @@ def __call__(self, *_):
         if isinstance(self.view.model(), QSortFilterProxyModel):
             selection = self.view.model().mapSelectionToSource(selection)
         values = [i.row() for i in selection.indexes()]
-        if values:
-            # FIXME: irrespective of PyListModel check, this might/should always
-            # callback with values!
-            if isinstance(self.model, PyListModel):
-                values = [self.model[i] for i in values]
-            if self.view.selectionMode() == self.view.SingleSelection:
-                values = values[0]
-            self.acyclic_setattr(values)
+
+        # set attribute's values
+        if isinstance(self.model, PyListModel):
+            values = [self.model[i] for i in values]
+        if self.view.selectionMode() == self.view.SingleSelection:
+            assert len(values) <= 1
+            values = values[0] if values else None
+        self.acyclic_setattr(values)
 
 
 class CallBackListBox:
diff --git a/Orange/widgets/tests/test_gui.py b/Orange/widgets/tests/test_gui.py
index 1d7d46b7325..6c385b7e975 100644
--- a/Orange/widgets/tests/test_gui.py
+++ b/Orange/widgets/tests/test_gui.py
@@ -1,3 +1,4 @@
+import unittest
 from unittest.mock import patch
 
 import numpy as np
@@ -55,6 +56,10 @@ def test_select_callback(self):
         view.setCurrentIndex(self.attrs.index(1, 0))
         self.assertEqual(widget.foo, [b])
 
+        # unselect all
+        sel_model.clear()
+        self.assertEqual(widget.foo, [])
+
     def test_select_callfront(self):
         widget = self.widget
         view = self.view
@@ -129,3 +134,7 @@ def test_argsort():
         test_array = np.array(["Bertha", "daniela", "ann", "Cecilia"])
         assert_equal(func(test_array, Qt.AscendingOrder), [2, 0, 3, 1])
         assert_equal(func(test_array, Qt.DescendingOrder), [1, 3, 0, 2])
+
+
+if __name__ == "__main__":
+    unittest.main()