make BranchAddressManager.getArrays() return None when the branch type is unknown
make BranchAddressManager.getArrays() return None when the branch type is unknown

alphatwirl/alphatwirl,TaiSakuma/AlphaTwirl,alphatwirl/alphatwirl,TaiSakuma/AlphaTwirl,alphatwirl/alphatwirl,alphatwirl/alphatwirl