Get an error when a node doesn't evaluate (#4693)
Get an error when a node doesn't evaluate (#4693)

Co-authored-by: Robert Kimball <f8f4fb0160c4e961c3d6afdbdcc40cfc21344ca8@intel.com>
NervanaSystems/ngraph,NervanaSystems/ngraph,NervanaSystems/ngraph,NervanaSystems/ngraph