null check dynamic casts #6297

Job	Run time
rust-check-git-rev-deps	19s
cargo-deny (advisories)	47s
build (gcc, current)	27m 1s
fmt	13s
build (gcc, current, --check-test-tx-meta)	15m 57s
cargo-deny (bans licenses sources)	43s
build (gcc, next)	27m 2s
build (gcc, next, --check-test-tx-meta)	16m 27s
build (clang, current)	25m 44s
build (clang, current, --check-test-tx-meta)	15m 53s
build (clang, next)	27m 4s
build (clang, next, --check-test-tx-meta)	17m 38s
complete	1s
	2h 54m 49s

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