In the short term, I would:

isVibrating = waveformParameters != null // may have just started
if (isVibrating) {
    waveformParameters.Shape = WaveformShape.Square;
    widget.UpdateWaveformParameters(waveformParameters);
}

In the longer term, unless there’s a good reason not to, I’d nudge the implementation towards having the code read more like:

widget.update(waveformParameters);

South Park made a good satire of exactly this, where Cartman immediately realized it meant he could continue being offensive and “safe space” away anything he didn’t want to acknowledge

Is it not an apt analogue to describe the behavior, though? After all, one well known failure mode of LLMs has been formally dubbed “hallucination”.