resource import controller: get_previous_imported_controller returns …

…None when no previous

src/robotide/controller/settingcontrollers.py

@@ -493,6 +493,7 @@ def publish_removed(self):
 class ResourceImportController(_ImportController):
     is_resource = True
     _resolved_import = False
+    _previous_imported_controller = None
 
     def set_value(self, name, args=None, alias=''):
         self._previous_imported_controller = self.get_imported_controller()

utest/controller/test_resource_import.py

@@ -63,12 +63,17 @@ def test_resource_import_knows_resource_after_import_has_been_removed(self):
         item_without_settings.imports.delete(0)
         self.assertEqual(self.new_resource, import_.get_imported_controller())
 
+    def test_previously_imported_resource_controller_is_none_by_default(self):
+        self._create_resource()
+        import_controller = self._add_resource_import_to_suite()
+        self.assertIsNone(import_controller.get_previous_imported_controller())
+
     @property
     def _keyword_controller(self):
         return self.ctrl.resources[-1].keywords[-1]
 
     def _add_resource_import_to_suite(self):
-        self.suite.imports.add_resource(self.res_name)
+        return self.suite.imports.add_resource(self.res_name)
 
     def _verify_unidentified_keyword(self):
         self._check_cells(ContentType.STRING, CellType.UNKNOWN)