Return early from Subst if replacement environments are empty (#5145)
Return early from Subst if replacement environments are empty (#5145)


cseed/hail,cseed/hail,cseed/hail,hail-is/hail,hail-is/hail,danking/hail,cseed/hail,danking/hail,danking/hail,cseed/hail,hail-is/hail,danking/hail,danking/hail,danking/hail,danking/hail,hail-is/hail,cseed/hail,cseed/hail,hail-is/hail,hail-is/hail,cseed/hail,hail-is/hail,hail-is/hail,danking/hail