fix: nullable parameters in DeclarativeMemoryItem #1299

Job	Run time
Collect changes / collect-changes	7s
Python tests / types-check	31s
Python tests / unit-tests (py311)	3m 32s
Python tests / unit-tests (py312)	2m 55s
Python tests / unit-tests (py310)	3m 18s
Python tests / unit-tests (py314)	2m 45s
Python tests / unit-tests (py313)	2m 46s
Python tests / lint-and-format-check	24s
status-check	3s
	16m 21s

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