Negative extents is null value not defect

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If you go into the Model [Sanity check], it says [Negative extents]. This is not a defect. The model of blizzard was also processed like this. it just null value
MinimumExtent { 3.40282e+038, 3.40282e+038, 3.40282e+038 },
MaximumExtent { -3.40282e+038, -3.40282e+038, -3.40282e+038 },