How to get Site Ground Temperature Building Surface

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I am writing a measure to add SiteGroundTemperatureBuildingSurface. When reporting the initial condition I tried to use the size method to check if there is a ground temperature surface object in the model, but the size method did not work, I tried to replace it with #empty?, #is_initialized but neither worked. Which method should be used to check if there is an existing ground temperature surface object?

ground_surface = model.getSiteGroundTemperatureBuildingSurface
ground_surface.size