Fix ifacmpeq/ne null handling #543

Job	Run time
rust_ci (macos-latest, stable)	44s
rust_ci (macos-latest, beta)	1m 11s
rust_ci (macos-latest, nightly)	1m 13s
rust_ci (ubuntu-latest, beta)	1m 23s
rust_ci (ubuntu-latest, stable)	43s
rust_ci (ubuntu-latest, nightly)	1m 20s
rust_ci (windows-latest, beta)	2m 42s
rust_ci (windows-latest, nightly)	2m 30s
rust_ci (windows-latest, stable)	2m 13s
	13m 59s

Provide feedback