Missing --null-input passthrough

[cbandy]

I like using long arguments in my scripts when they seem more legible than short ones. I was surprised to find that yq supports jq's -n but not its equivalent --null-input.

$ python3 -m yq -n .
null

$ python3 -m yq --null-input .
usage: yq [options] <jq filter> [input file...]
…

$ jq --null-input .
null

$ python3 -m yq --version
yq 3.4.3
$ jq --version
jq-1.7.1