One feature I found very useful when using jq in Bash is the "alternative operator" '//'.

  result=$(echo "$data" | jq -r '.optional // ""')
  if [[ -n "$result" ]] ...

feels more natural in Bash than

  result=$(echo "$data" | jq -r '.optional')
  if [[ "$result" != null ]] ...

Especially if an empty field should be handled the same way.

And when using the raw-output option it helps with the ambiguity between "null" and null.