fixing swift config fetching in registrar

core/registrar/config.py

@@ -20,9 +20,13 @@ def constructor_env_variables(loader, node):
         if match:
             full_value = value
             for g in match:
-                full_value = full_value.replace(
-                    f'${{{g}}}', os.environ.get(g, g)
-                )
+                env_variable = os.environ.get(g, )
+                if env_variable is not None:
+                    full_value = full_value.replace(
+                        f'${{{g}}}', env_variable
+                    )
+                else:
+                    return None
             return full_value
         return value