Java: Fix lpopCount null handling #5686

Job	Run time
get-matrices	3s
get-matrices	3s
lint-rust	4m 5s
lint-rust	4m 5s
get-containers	0s
get-containers	0s
Modules Tests	1s
Modules Tests	0s
test-java-container	0s
test-java-container	0s
test-java (17, valkey, 8.0, always, ubuntu, linux, ubuntu-latest, x64, x86_64-unknown-linux-gnu, ...	19m 40s
test-java (17, valkey, 8.0, always, ubuntu, linux, ubuntu-latest, x64, x86_64-unknown-linux-gnu, ...	18m 53s
test-java (17, redis, 6.2, always, ubuntu, linux, ubuntu-latest, x64, x86_64-unknown-linux-gnu, p...	16m 48s
test-java (17, redis, 6.2, always, ubuntu, linux, ubuntu-latest, x64, x86_64-unknown-linux-gnu, p...	16m 48s
	1h 20m 26s

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