Throw eInvalidExtents when missing fonts

[sdphg]

When I call the BlockReference's GeometricExtents, it throw a eInvalidExtents exception. After some check, I found when the drawing have some fonts that not exist in my computer the exception occur or it works find. Does anybody know why? and how to avoid this exception.THX. 

[fsztuczny]

Extents3d? bBox = ent.Bounds;
if( bBox != null )
{
   ...
}