load custom world in gazebo from launch file

Hello everyone, I've built a custom wold for gazebo (dae file) and I'm trying to load this file from a launch file. When I run the world file directly from gazebo, it woks and I can see the world (gazebo maze.world). But when I build a launch file and include the world file inside the launch file, I get the following error: Error [SystemPaths.cc:367] File or path does not exist[""] Error [Visual.cc:2138] No mesh specified Here is the content of the world file (maze.world):  and here is the launch file(maze.launch):  both launch file and world file are in the same directory and I've set the GAZEBO_MODEL_PATH to that directory. Can someone tell me what's the problem here? Thanks