fix image height, null check #895

	# docker continuous delivery
	# deliver docker images to configured repo with tags to match branches and git tags
	---
	name: Publish Docker
	on: [push]
	jobs:
	build:
	runs-on: ubuntu-latest
	steps:
	- name: Checkout git commit
	uses: actions/checkout@master
	with:
	fetch-depth: 0

	- name: Set environment variable for version from git output
	run: echo "REACT_APP_VERSION_STRING=$(git describe --always --tags)" >> $GITHUB_ENV

	- name: Publish to Dockerhub registry
	# todo: pin to hash
	uses: elgohr/Publish-Docker-Github-Action@master
	with:
	# https://help.github.com/en/actions/reference/context-and-expression-syntax-for-github-actions
	name: ${{ secrets.DOCKER_REPO }}
	# configured at repo settings/secrets
	username: ${{ secrets.DOCKER_USERNAME }}
	password: ${{ secrets.DOCKER_PASSWORD }}
	# create docker image tags to match git tags
	tag_names: true
	buildargs: REACT_APP_VERSION_STRING

Provide feedback