[KQP RBO] Aggregation add support empty keys

[denis0x0D]

Changelog entry

#27661

Changelog category

• Not for changelog (changelog entry is not required)

Description for reviewers

...

[github-actions]

🟢 2025-10-27 16:04:56 UTC The validation of the Pull Request description is successful.

[github-actions]

⚪ 2025-10-27 15:32:46 UTC Pre-commit check linux-x86_64-relwithdebinfo for 0f8c519 has started.
⚪ 2025-10-27 15:33:16 UTC Artifacts will be uploaded here
⚪ 2025-10-27 15:35:15 UTC ya make is running...
⚫ 2025-10-27 15:41:20 UTC Check cancelled

[github-actions]

⚪ 2025-10-27 15:33:36 UTC Pre-commit check linux-x86_64-release-asan for 0f8c519 has started.
⚪ 2025-10-27 15:33:50 UTC Artifacts will be uploaded here
⚪ 2025-10-27 15:35:11 UTC ya make is running...
⚫ 2025-10-27 15:41:26 UTC Check cancelled

[github-actions]

⚪ 2025-10-27 15:46:33 UTC Pre-commit check linux-x86_64-relwithdebinfo for 22948dd has started.
⚪ 2025-10-27 15:46:47 UTC Artifacts will be uploaded here
⚪ 2025-10-27 15:48:13 UTC ya make is running...
🟡 2025-10-27 17:13:36 UTC Some tests failed, follow the links below. Going to retry failed tests...

Ya make output | Test bloat

TESTS	PASSED	ERRORS	FAILED	SKIPPED	MUTED?
38552	35741	0	1	2787	23

⚪ 2025-10-27 17:13:47 UTC ya make is running... (failed tests rerun, try 2)
🟢 2025-10-27 17:30:05 UTC Tests successful.

Ya make output | Test bloat | Test bloat

TESTS	PASSED	ERRORS	FAILED	SKIPPED	MUTED?
445 (only retried tests)	425	0	0	0	20

🟢 2025-10-27 17:30:08 UTC Build successful.
🟢 2025-10-27 17:30:23 UTC ydbd size 2.3 GiB changed* by +9.3 KiB, which is < 100.0 KiB vs main: OK

ydbd size dash	main: c2e9bc8	merge: 22948dd	diff	diff %
ydbd size	2 440 232 848 Bytes	2 440 242 360 Bytes	+9.3 KiB	+0.000%
ydbd stripped size	518 956 040 Bytes	518 954 632 Bytes	-1.4 KiB	-0.000%

^{*please be aware that the difference is based on comparing your commit and the last completed build from the post-commit, check comparation}

[github-actions]

⚪ 2025-10-27 15:46:37 UTC Pre-commit check linux-x86_64-release-asan for 22948dd has started.
⚪ 2025-10-27 15:46:52 UTC Artifacts will be uploaded here
⚪ 2025-10-27 15:48:18 UTC ya make is running...
🟡 2025-10-27 17:54:45 UTC Some tests failed, follow the links below. This fail is not in blocking policy yet

Ya make output | Test bloat

TESTS	PASSED	ERRORS	FAILED	SKIPPED	MUTED?
15284	14771	0	215	280	18

🟢 2025-10-27 17:54:51 UTC Build successful.
🟢 2025-10-27 17:55:15 UTC ydbd size 3.8 GiB changed* by +16.1 KiB, which is < 100.0 KiB vs main: OK

ydbd size dash	main: c2e9bc8	merge: 22948dd	diff	diff %
ydbd size	4 061 040 592 Bytes	4 061 057 056 Bytes	+16.1 KiB	+0.000%
ydbd stripped size	1 508 772 032 Bytes	1 508 771 328 Bytes	-704 Bytes	-0.000%

^{*please be aware that the difference is based on comparing your commit and the last completed build from the post-commit, check comparation}