prevent undefined exception on undo of attach new aT
prevent undefined exception on undo of attach new aT

Masoumeh/arethusa,fbaumgardt/arethusa,latin-language-toolkit/arethusa,PonteIneptique/arethusa,fbaumgardt/arethusa,alpheios-project/arethusa,latin-language-toolkit/arethusa,Masoumeh/arethusa,alpheios-project/arethusa,fbaumgardt/arethusa,alpheios-project/arethusa,PonteIneptique/arethusa