improve the docs on general_null #1335

	name: docs build

	on:
	push:
	branches:
	- development
	- main
	pull_request:
	branches:
	- development

	jobs:
	docs:
	runs-on: ubuntu-latest

	steps:
	- uses: actions/checkout@v3
	with:
	fetch-depth: 0
	- name: Install pandoc and doxygen
	run: \|
	sudo apt install pandoc doxygen

	- name: Setup Python
	uses: actions/setup-python@v4
	with:
	python-version: '3.10'

	- name: Cache pip
	uses: actions/cache@v3
	with:
	# this path is specific to Ubuntu
	path: ~/.cache/pip
	key: ${{ runner.os }}-pip-${{ hashFiles('**/requirements.txt') }}
	restore-keys: \|
	${{ runner.os }}-pip-

	- name: Install dependencies
	run: pip install -r ./requirements.txt

	- name: Build docs
	run: \|
	cd sphinx_docs/
	make SPHINXOPTS=-v html

	- name: Link check
	run: \|
	cd sphinx_docs/
	make SPHINXOPTS=-v linkcheck

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