In bash-5.2, using the ${parameter@Q} parameter expansion with an unset
parameter, in an array subscript, in an arithmetic context, causes a
segmentation fault.
bash-5.1$ ./bash --norc
bash-5.2$ (x[y[${a@Q}]]=)
Segmentation fault (core dumped)
bash-5.2$ ( (( y[${a@Q}] )) )
Segmentation fault (core dumped)
bash-5.2$ a=
bash-5.2$ (x[y[${a@Q}]]=)
bash: \'\': syntax error: operand expected (error token is "\'\'")
bash-5.2$ ( (( y[${a@Q}] )) )
bash: \'\': syntax error: operand expected (error token is "\'\'")
