Unable to cast Zilean ult on a friendly champion with zhonya's

Zhonya's was changed awhile back to allow for healing from teammates even while they are in stasis. However, an ally is still untargetable by Zilean's ult which is counterproductive, and I believe should be changed to work like healing does. I normally smart+self cast my abilities and one of the most annoying things is to ult a low health ally at the same time that they use Zhonya's just to end up wasting it by ulting myself because they were no longer targetable.

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