Yep, originally I had set it to zero because it made sense that it should “default” to that if not provided (i.e. the exponent w/ linear function then follows the “basic” formulation). But I realized it was to avoid the divide by 0 so had changed it to 1e-6.
I tend to agree that it’s cleaner to make it be 0 (as long as implementers are warned that they should protect against that case).
Thanks.