Add support for null in yaml tests.

[bzbarsky-apple]

Adds support for sending null as a command argument and for null in
the expected value.

Problem

Can't test things involving null values in yaml.

Change overview

Add support for it.

Testing

Tests are modified to exercise this functionality in a simple case.

[github-actions]

PR #11139: Size comparison from 149e582 to af99537

Increases (5 builds for esp32, linux, mbed)

platform	target	config	section	149e582	af99537	change	% change
esp32	all-clusters-app	c3devkit	(read only)	875926	876026	100	0.0
			.flash.text	875926	876026	100	0.0
		m5stack	(read only)	907275	907411	136	0.0
			.flash.text	907275	907411	136	0.0
linux	all-clusters-app	debug	(read only)	1653505	1654161	656	0.0
			.text	1383346	1384002	656	0.0
	chip-tool	debug	(read only)	4262469	4265077	2608	0.1
			.rodata	214032	214320	288	0.1
			.text	3785589	3787909	2320	0.1
mbed	all-clusters-app	CY8CPROTO_062_4343W+release	(read/write)	2290664	2290728	64	0.0
			.text	1253264	1253328	64	0.0

Full report (37 builds for efr32, esp32, k32w, linux, mbed, nrfconnect, p6, qpg, telink)

platform	target	config	section	149e582	af99537	change	% change
efr32	lighting-app	BRD4161A	(read only)	737476	737476	0	0.0
			(read/write)	115428	115428	0	0.0
			.bss	113676	113676	0	0.0
			.data	1752	1752	0	0.0
			.text	737468	737468	0	0.0
		BRD4161A+rpc	(read only)	724916	724916	0	0.0
			(read/write)	132032	132032	0	0.0
			.bss	130180	130180	0	0.0
			.data	1852	1852	0	0.0
			.text	724908	724908	0	0.0
	lock-app	BRD4161A	(read only)	716756	716756	0	0.0
			(read/write)	113244	113244	0	0.0
			.bss	111532	111532	0	0.0
			.data	1712	1712	0	0.0
			.text	716748	716748	0	0.0
	window-app	BRD4161A	(read only)	717660	717660	0	0.0
			(read/write)	113568	113568	0	0.0
			.bss	111852	111852	0	0.0
			.data	1716	1716	0	0.0
			.text	717652	717652	0	0.0
esp32	all-clusters-app	c3devkit	(read only)	875926	876026	100	0.0
			(read/write)	1308672	1308672	0	0.0
			.dram0.bss	59248	59248	0	0.0
			.dram0.data	16448	16448	0	0.0
			.flash.rodata	199744	199744	0	0.0
			.flash.text	875926	876026	100	0.0
			.iram0.text	57554	57554	0	0.0
		m5stack	(read only)	907275	907411	136	0.0
			(read/write)	428460	428460	0	0.0
			.dram0.bss	61744	61744	0	0.0
			.dram0.data	32084	32084	0	0.0
			.flash.rodata	208468	208468	0	0.0
			.flash.text	907275	907411	136	0.0
			.iram0.text	125115	125115	0	0.0
k32w	lighting-app	k32w061+se05x+release	(read/write)	701024	701024	0	0.0
			.bss	78688	78688	0	0.0
			.data	1900	1900	0	0.0
			.text	614636	614636	0	0.0
	lock-app	k32w061+debug	(read/write)	592980	592980	0	0.0
			.bss	69172	69172	0	0.0
			.data	1864	1864	0	0.0
			.text	516144	516144	0	0.0
	shell	k32w061+debug	(read/write)	425252	425252	0	0.0
			.bss	63256	63256	0	0.0
			.data	672	672	0	0.0
			.text	359620	359620	0	0.0
linux	all-clusters-app	debug	(read only)	1653505	1654161	656	0.0
			(read/write)	119136	119136	0	0.0
			.bss	51376	51376	0	0.0
			.data	978	978	0	0.0
			.data.rel.ro	61536	61536	0	0.0
			.dynamic	592	592	0	0.0
			.got	4088	4088	0	0.0
			.init	27	27	0	0.0
			.init_array	520	520	0	0.0
			.rodata	137845	137845	0	0.0
			.text	1383346	1384002	656	0.0
	bridge-app	debug+rpc	(read only)	1282421	1282421	0	0.0
			(read/write)	85192	85192	0	0.0
			.bss	51856	51856	0	0.0
			.data	976	976	0	0.0
			.data.rel.ro	27368	27368	0	0.0
			.dynamic	592	592	0	0.0
			.got	3952	3952	0	0.0
			.init	27	27	0	0.0
			.init_array	400	400	0	0.0
			.rodata	110812	110812	0	0.0
			.text	1076245	1076245	0	0.0
	chip-tool	debug	(read only)	4262469	4265077	2608	0.1
			(read/write)	122208	122208	0	0.0
			.bss	17680	17680	0	0.0
			.data	1584	1584	0	0.0
			.data.rel.ro	97536	97536	0	0.0
			.dynamic	592	592	0	0.0
			.got	4368	4368	0	0.0
			.init	27	27	0	0.0
			.init_array	424	424	0	0.0
			.rodata	214032	214320	288	0.1
			.text	3785589	3787909	2320	0.1
	lighting-app	debug+rpc	(read only)	1541401	1541401	0	0.0
			(read/write)	102032	102032	0	0.0
			.bss	41208	41208	0	0.0
			.data	1106	1106	0	0.0
			.data.rel.ro	54448	54448	0	0.0
			.dynamic	608	608	0	0.0
			.got	4112	4112	0	0.0
			.init	27	27	0	0.0
			.init_array	528	528	0	0.0
			.rodata	128977	128977	0	0.0
			.text	1279922	1279922	0	0.0
	ota-provider-app	debug	(read only)	1238937	1238937	0	0.0
			(read/write)	67904	67904	0	0.0
			.bss	37440	37440	0	0.0
			.data	752	752	0	0.0
			.data.rel.ro	24616	24616	0	0.0
			.dynamic	592	592	0	0.0
			.got	4016	4016	0	0.0
			.init	27	27	0	0.0
			.init_array	440	440	0	0.0
			.rodata	110984	110984	0	0.0
			.text	1031730	1031730	0	0.0
	ota-requestor-app	debug	(read only)	1301033	1301033	0	0.0
			(read/write)	76648	76648	0	0.0
			.bss	45216	45216	0	0.0
			.data	816	816	0	0.0
			.data.rel.ro	25496	25496	0	0.0
			.dynamic	592	592	0	0.0
			.got	3984	3984	0	0.0
			.init	27	27	0	0.0
			.init_array	512	512	0	0.0
			.rodata	127680	127680	0	0.0
			.text	1075490	1075490	0	0.0
	shell	debug	(read only)	787361	787361	0	0.0
			(read/write)	57792	57792	0	0.0
			.bss	16168	16168	0	0.0
			.data	242	242	0	0.0
			.data.rel.ro	36880	36880	0	0.0
			.dynamic	592	592	0	0.0
			.got	3528	3528	0	0.0
			.init	27	27	0	0.0
			.init_array	336	336	0	0.0
			.rodata	77519	77519	0	0.0
			.text	608258	608258	0	0.0
	tv-app	debug	(read only)	1774529	1774529	0	0.0
			(read/write)	289656	289656	0	0.0
			.bss	223280	223280	0	0.0
			.data	2032	2032	0	0.0
			.data.rel.ro	58704	58704	0	0.0
			.dynamic	592	592	0	0.0
			.got	4408	4408	0	0.0
			.init	27	27	0	0.0
			.init_array	608	608	0	0.0
			.rodata	154776	154776	0	0.0
			.text	1477442	1477442	0	0.0
mbed	all-clusters-app	CY8CPROTO_062_4343W+release	(read only)	6224	6224	0	0.0
			(read/write)	2290664	2290728	64	0.0
			.bss	180620	180620	0	0.0
			.data	5192	5192	0	0.0
			.heap	850632	850632	0	0.0
			.text	1253264	1253328	64	0.0
	lighting-app	CY8CPROTO_062_4343W+release	(read only)	6224	6224	0	0.0
			(read/write)	2274992	2274992	0	0.0
			.bss	172820	172820	0	0.0
			.data	5568	5568	0	0.0
			.heap	858056	858056	0	0.0
			.text	1237592	1237592	0	0.0
	lock-app	CY8CPROTO_062_4343W+release	(read only)	6224	6224	0	0.0
			(read/write)	2252712	2252712	0	0.0
			.bss	171724	171724	0	0.0
			.data	5552	5552	0	0.0
			.heap	859168	859168	0	0.0
			.text	1215312	1215312	0	0.0
	pigweed-app	CY8CPROTO_062_4343W+release	(read only)	6224	6224	0	0.0
			(read/write)	1139744	1139744	0	0.0
			.bss	11752	11752	0	0.0
			.data	4368	4368	0	0.0
			.heap	1020328	1020328	0	0.0
			.text	103128	103128	0	0.0
	shell	CY8CPROTO_062_4343W+release	(read only)	6224	6224	0	0.0
			(read/write)	2048984	2048984	0	0.0
			.bss	156208	156208	0	0.0
			.data	4968	4968	0	0.0
			.heap	875272	875272	0	0.0
			.text	1011584	1011584	0	0.0
nrfconnect	lighting-app	nrf52840dk_nrf52840	(read/write)	862911	862911	0	0.0
			bss	112132	112132	0	0.0
			rodata	97528	97528	0	0.0
			text	577624	577624	0	0.0
		nrf52840dk_nrf52840+rpc	(read/write)	823735	823735	0	0.0
			bss	108372	108372	0	0.0
			rodata	88304	88304	0	0.0
			text	550800	550800	0	0.0
		nrf5340dk_nrf5340_cpuapp	(read/write)	787902	787902	0	0.0
			bss	113504	113504	0	0.0
			rodata	92768	92768	0	0.0
			text	507092	507092	0	0.0
	lock-app	nrf52840dk_nrf52840	(read/write)	839583	839583	0	0.0
			bss	111168	111168	0	0.0
			rodata	93880	93880	0	0.0
			text	559108	559108	0	0.0
		nrf5340dk_nrf5340_cpuapp	(read/write)	764882	764882	0	0.0
			bss	112576	112576	0	0.0
			rodata	89188	89188	0	0.0
			text	488668	488668	0	0.0
	pigweed-app	nrf52840dk_nrf52840	(read/write)	497323	497323	0	0.0
			bss	51824	51824	0	0.0
			rodata	45776	45776	0	0.0
			text	339436	339436	0	0.0
	pump-app	nrf52840dk_nrf52840	(read/write)	844287	844287	0	0.0
			bss	111304	111304	0	0.0
			rodata	95128	95128	0	0.0
			text	562320	562320	0	0.0
	pump-controller-app	nrf52840dk_nrf52840	(read/write)	839575	839575	0	0.0
			bss	111200	111200	0	0.0
			rodata	93904	93904	0	0.0
			text	558952	558952	0	0.0
	shell	nrf52840dk_nrf52840	(read/write)	776435	776435	0	0.0
			bss	109072	109072	0	0.0
			rodata	72536	72536	0	0.0
			text	520236	520236	0	0.0
		nrf5340dk_nrf5340_cpuapp	(read/write)	691490	691490	0	0.0
			bss	110056	110056	0	0.0
			rodata	67180	67180	0	0.0
			text	440848	440848	0	0.0
p6	lock-app	default	(read/write)	2169096	2169096	0	0.0
			.bss	67168	67168	0	0.0
			.data	2416	2416	0	0.0
			.heap	963760	963760	0	0.0
			.text	1127360	1127360	0	0.0
qpg	lighting-app	qpg6100+debug	(read only)	491224	491224	0	0.0
			(read/write)	114144	114144	0	0.0
			.bss	51288	51288	0	0.0
			.data	1000	1000	0	0.0
			.text	485904	485904	0	0.0
	lock-app	qpg6100+debug	(read only)	467556	467556	0	0.0
			(read/write)	114140	114140	0	0.0
			.bss	50240	50240	0	0.0
			.data	956	956	0	0.0
			.text	462236	462236	0	0.0
	persistent-storage-app	qpg6100+debug	(read only)	155244	155244	0	0.0
			(read/write)	114140	114140	0	0.0
			.bss	27752	27752	0	0.0
			.data	372	372	0	0.0
			.text	149924	149924	0	0.0
telink	lighting-app	tlsr9518adk80d	(read/write)	664518	664518	0	0.0
			bss	69944	69944	0	0.0
			noinit	33216	33216	0	0.0
			text	458068	458068	0	0.0

[woody-apple]

Fast tracking this to unblock testing.