remove a compilation warning when no transform is present
remove a compilation warning when no transform is present

rdebroiz/medInria-public,NicolasSchnitzler/medInria-public,rdebroiz/medInria-public,aabadie/medInria-public,rdebroiz/medInria-public,aabadie/medInria-public,aabadie/medInria-public,NicolasSchnitzler/medInria-public,NicolasSchnitzler/medInria-public