[FIX] FeatureConstructor: Fix crash when new variable is created without data

Orange/widgets/data/owfeatureconstructor.py

@@ -168,7 +168,7 @@ def setEditorData(self, data, domain):
         self.setModified(False)
         self.featureChanged.emit()
         self.attrs_model[:] = ["Select Feature"]
-        if domain or domain.metas:
+        if domain is not None and (domain or domain.metas):
             self.attrs_model[:] += chain(domain.attributes,
                                          domain.class_vars,
                                          domain.metas)

Orange/widgets/data/tests/test_owfeatureconstructor.py

@@ -4,16 +4,18 @@
 
 from Orange.data import (Table, Domain, StringVariable,
                          ContinuousVariable, DiscreteVariable)
+from Orange.widgets.tests.base import WidgetTest
 from Orange.widgets.utils.itemmodels import PyListModel
 from Orange.widgets.data.owfeatureconstructor import (DiscreteDescriptor,
                                                       ContinuousDescriptor,
                                                       StringDescriptor,
-                                                      construct_variables)
+                                                      construct_variables, OWFeatureConstructor)
 
 from Orange.widgets.data.owfeatureconstructor import (
     freevars, make_lambda, validate_exp
 )
 
+
 class FeatureConstructorTest(unittest.TestCase):
     def test_construct_variables_discrete(self):
         data = Table("iris")
@@ -175,3 +177,12 @@ def validate_(source):
 
         with self.assertRaises(ValueError):
             validate_("{a:1 for a in s}")
+
+
+class OWFeatureConstructorTests(WidgetTest):
+    def setUp(self):
+        self.widget = OWFeatureConstructor()
+
+    def test_create_variable_with_no_data(self):
+        self.widget.addFeature(
+            ContinuousDescriptor("X1", "", 3))