Add the 0% likelihood option after avoiding a risk

Customer is suggesting to add another likelihood level in the residual likelihood part of the risk management.

Example:

Risk A was reviewed and it's treatment strategy is avoidance. The risk was removed completely. Nevertheless the residual risk likelihood can be set only to "low" "medium" or "high" or "critical".

Customer is aware that the "low" level refers to risk with less than 20% chance of happening, would however like to see an 5th option, expressing the 0% likelihood.