Open/close world via messages

edit

I looked through the Messages API and tried to use WorldModify messages like this:

• send a WorldModify message with remove set to true and world_name set to default to close the current world (also tried to reference the world with "worlds/empty.world")
• send a WorldModify message with create set to true and world_name set to, for example, worlds/pioneer2dx.world in order to open a new world

The result is that if I have the client open it crashes, otherwise (if gazebo is running headless) nothing changes. I have also tried to first pause the world then send the WorldModify messages and then do a reset with a WorldReset message but again nothing happened. I check with gz topic -e /gazebo/world/modify that gazebo receives the messages, so I guess I'm not using them properly.

Is it possible to open/close worlds via messages? If it is, how do you do that?