test: add empty context test

Author: rpenido

xblock/test/test_field_data.py

@@ -76,6 +76,13 @@ def test_invalid_scope(self):
         with pytest.raises(InvalidScopeError):
             self.split.get(self.block, 'user_state')
 
+    def test_empty_scope(self):
+        with pytest.raises(InvalidScopeError):
+            split = SplitFieldData({
+                Scope.user_state: None
+            })
+            split.get(self.block, 'user_state')
+
     def test_default(self):
         self.split.default(self.block, 'content')
         self.content.default.assert_called_once_with(self.block, 'content')