$aa=[ {qq=>{rr=>1}} ];

DB<16> p defined($aa->{pippo})
No such pseudo-hash field "pippo" at (eval 19)

DB<17> p defined($aa->{qq})

DB<18> p defined($aa->{pippo}->{lillo})
No such pseudo-hash field "pippo" at (eval 21)

DB<19> p defined($aa->{qq}->{lillo})