spec: allow record {} <: record {null} #378

	name: Rust Bench
	on:
	pull_request:
	paths:
	- 'rust/**'
	jobs:
	runBenchMark:
	name: run benchmark
	runs-on: ubuntu-latest
	steps:
	- uses: actions/checkout@v2
	with:
	fetch-depth: 0
	- name: Install stable toolchain
	uses: actions-rs/toolchain@v1
	with:
	profile: minimal
	toolchain: stable
	override: true
	- name: Cache cargo build
	uses: actions/cache@v2
	with:
	path: \|
	~/.cargo/registry
	~/.cargo/git
	target
	key: ${{ runner.os }}-bench-${{ hashFiles('**/Cargo.lock') }}
	- uses: boa-dev/criterion-compare-action@master
	with:
	cwd: rust/candid
	benchName: benchmark # needed to address https://bheisler.github.io/criterion.rs/book/faq.html#cargo-bench-gives-unrecognized-option-errors-for-valid-command-line-options
	branchName: ${{ github.base_ref }}
	token: ${{ secrets.GITHUB_TOKEN }}

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