Release v4.108.0

Changed

• Stage now renders commands with an optional scalar concept property whose validation rules all accept absence (comparisons, length and matches). An absent value is accepted and a present value is validated exactly as Screenplay specifies. Optional concepts with absence-rejecting rules such as not empty, optional collections of validated concepts and optional named-value concepts are still refused with STAGE-ESM-005, and the message now says which of these applies. (#409)