setRange on IsoContour gives NullPointerException

when i try to call setRange on an IsoContour I get a
NullPointerException.  Specifically it happens at line 435 of

      ((ContourControl) control).getMainContours(bvalues, values);

It would seem that "control" is null at this point.  The general context
of this is that I am adding the ranges of Display objects to what is
saved by the SpreadSheet's save function.  When I try to open a
SpreadSheet file containing a cell which has data mapped to IsoContour,
when I get to the point in my code where I call setRange on that map, I
get the above exception.