Add support to chip-tool for sending the null value for nullable arguments.

[bzbarsky-apple]

It's represented as "null" on the command line.

Warning: this might make it difficult to send the string value "null"
for a nullable char string.

Problem

Can't set attributes to null via chip-tool command line, or set null for nullable command arguments.

Change overview

See above.

Testing

Manually tested that I can set the nullable-boolean and nullable-char-string attributes of TestCluster to both null and non-null values.

[github-actions]

PR #12653: Size comparison from 7871953 to 0932cd9

Increases above 0.2%:

platform	target	config	section	7871953	0932cd9	change	% change
linux	chip-tool	debug	(read only)	6651717	6670677	18960	0.3
			.text	5933045	5952005	18960	0.3

Increases (1 build for linux)

platform	target	config	section	7871953	0932cd9	change	% change
linux	chip-tool	debug	(read only)	6651717	6670677	18960	0.3
			.text	5933045	5952005	18960	0.3

Full report (39 builds for efr32, esp32, k32w, linux, mbed, nrfconnect, p6, qpg, telink)

platform	target	config	section	7871953	0932cd9	change	% change
efr32	lighting-app	BRD4161A	(read only)	796540	796540	0	0.0
			(read/write)	120740	120740	0	0.0
			.bss	118912	118912	0	0.0
			.data	1828	1828	0	0.0
			.text	796532	796532	0	0.0
		BRD4161A+rpc	(read only)	824508	824508	0	0.0
			(read/write)	139048	139048	0	0.0
			.bss	137112	137112	0	0.0
			.data	1936	1936	0	0.0
			.text	824500	824500	0	0.0
	lock-app	BRD4161A	(read only)	771224	771224	0	0.0
			(read/write)	118680	118680	0	0.0
			.bss	116888	116888	0	0.0
			.data	1788	1788	0	0.0
			.text	771216	771216	0	0.0
	window-app	BRD4161A	(read only)	773496	773496	0	0.0
			(read/write)	118880	118880	0	0.0
			.bss	117088	117088	0	0.0
			.data	1792	1792	0	0.0
			.text	773488	773488	0	0.0
esp32	all-clusters-app	c3devkit	(read only)	856134	856134	0	0.0
			(read/write)	1298882	1298882	0	0.0
			.dram0.bss	61424	61424	0	0.0
			.dram0.data	14132	14132	0	0.0
			.flash.rodata	170288	170288	0	0.0
			.flash.text	856134	856134	0	0.0
			.iram0.text	62076	62076	0	0.0
		m5stack	(read only)	960427	960427	0	0.0
			(read/write)	443256	443256	0	0.0
			.dram0.bss	68776	68776	0	0.0
			.dram0.data	34056	34056	0	0.0
			.flash.rodata	208636	208636	0	0.0
			.flash.text	955043	955043	0	0.0
			.iram0.text	123451	123451	0	0.0
k32w	lighting-app	k32w061+se05x+release	(read/write)	731592	731592	0	0.0
			.bss	79408	79408	0	0.0
			.data	1860	1860	0	0.0
			.text	644524	644524	0	0.0
	lock-app	k32w061+debug	(read/write)	622308	622308	0	0.0
			.bss	70072	70072	0	0.0
			.data	1828	1828	0	0.0
			.text	544608	544608	0	0.0
	shell	k32w061+debug	(read/write)	688216	688216	0	0.0
			.bss	81720	81720	0	0.0
			.data	1800	1800	0	0.0
			.text	598896	598896	0	0.0
linux	all-clusters-app	debug	(read only)	1902129	1902129	0	0.0
			(read/write)	128712	128712	0	0.0
			.bss	54064	54064	0	0.0
			.data	1216	1216	0	0.0
			.data.rel.ro	67968	67968	0	0.0
			.dynamic	592	592	0	0.0
			.got	4120	4120	0	0.0
			.init	27	27	0	0.0
			.init_array	720	720	0	0.0
			.rodata	154933	154933	0	0.0
			.text	1601666	1601666	0	0.0
	bridge-app	debug+rpc	(read only)	1450789	1450789	0	0.0
			(read/write)	74904	74904	0	0.0
			.bss	36464	36464	0	0.0
			.data	1728	1728	0	0.0
			.data.rel.ro	31632	31632	0	0.0
			.dynamic	592	592	0	0.0
			.got	3992	3992	0	0.0
			.init	27	27	0	0.0
			.init_array	480	480	0	0.0
			.rodata	122692	122692	0	0.0
			.text	1223029	1223029	0	0.0
	chip-tool	debug	(read only)	6651717	6670677	18960	0.3
			(read/write)	200040	200040	0	0.0
			.bss	34728	34728	0	0.0
			.data	1024	1024	0	0.0
			.data.rel.ro	158600	158600	0	0.0
			.dynamic	592	592	0	0.0
			.got	4496	4496	0	0.0
			.init	27	27	0	0.0
			.init_array	568	568	0	0.0
			.rodata	313777	313777	0	0.0
			.text	5933045	5952005	18960	0.3
	lighting-app	debug+rpc	(read only)	1736569	1736569	0	0.0
			(read/write)	107968	107968	0	0.0
			.bss	42160	42160	0	0.0
			.data	1280	1280	0	0.0
			.data.rel.ro	59136	59136	0	0.0
			.dynamic	608	608	0	0.0
			.got	4144	4144	0	0.0
			.init	27	27	0	0.0
			.init_array	616	616	0	0.0
			.rodata	143281	143281	0	0.0
			.text	1450450	1450450	0	0.0
	ota-provider-app	debug	(read only)	1408089	1408089	0	0.0
			(read/write)	73104	73104	0	0.0
			.bss	39040	39040	0	0.0
			.data	928	928	0	0.0
			.data.rel.ro	27944	27944	0	0.0
			.dynamic	592	592	0	0.0
			.got	4056	4056	0	0.0
			.init	27	27	0	0.0
			.init_array	520	520	0	0.0
			.rodata	124078	124078	0	0.0
			.text	1179154	1179154	0	0.0
	ota-requestor-app	debug	(read only)	1517409	1517409	0	0.0
			(read/write)	78152	78152	0	0.0
			.bss	42208	42208	0	0.0
			.data	992	992	0	0.0
			.data.rel.ro	29720	29720	0	0.0
			.dynamic	592	592	0	0.0
			.got	4064	4064	0	0.0
			.init	27	27	0	0.0
			.init_array	544	544	0	0.0
			.rodata	136823	136823	0	0.0
			.text	1271778	1271778	0	0.0
	shell	debug	(read only)	823577	823577	0	0.0
			(read/write)	60616	60616	0	0.0
			.bss	16936	16936	0	0.0
			.data	256	256	0	0.0
			.data.rel.ro	38936	38936	0	0.0
			.dynamic	592	592	0	0.0
			.got	3520	3520	0	0.0
			.init	27	27	0	0.0
			.init_array	344	344	0	0.0
			.rodata	84754	84754	0	0.0
			.text	631986	631986	0	0.0
	tv-app	debug	(read only)	2054553	2054553	0	0.0
			(read/write)	320320	320320	0	0.0
			.bss	247480	247480	0	0.0
			.data	2768	2768	0	0.0
			.data.rel.ro	64240	64240	0	0.0
			.dynamic	592	592	0	0.0
			.got	4456	4456	0	0.0
			.init	27	27	0	0.0
			.init_array	736	736	0	0.0
			.rodata	175436	175436	0	0.0
			.text	1724210	1724210	0	0.0
mbed	all-clusters-app	CY8CPROTO_062_4343W+release	(read only)	6224	6224	0	0.0
			(read/write)	2316272	2316272	0	0.0
			.bss	184596	184596	0	0.0
			.data	5240	5240	0	0.0
			.heap	846608	846608	0	0.0
			.text	1278848	1278848	0	0.0
	lighting-app	CY8CPROTO_062_4343W+release	(read only)	6224	6224	0	0.0
			(read/write)	2299968	2299968	0	0.0
			.bss	173400	173400	0	0.0
			.data	5496	5496	0	0.0
			.heap	857552	857552	0	0.0
			.text	1262568	1262568	0	0.0
	lock-app	CY8CPROTO_062_4343W+release	(read only)	6224	6224	0	0.0
			(read/write)	2273072	2273072	0	0.0
			.bss	172440	172440	0	0.0
			.data	5496	5496	0	0.0
			.heap	858512	858512	0	0.0
			.text	1235672	1235672	0	0.0
	pigweed-app	CY8CPROTO_062_4343W+release	(read only)	6224	6224	0	0.0
			(read/write)	1140008	1140008	0	0.0
			.bss	11756	11756	0	0.0
			.data	4376	4376	0	0.0
			.heap	1020312	1020312	0	0.0
			.text	103392	103392	0	0.0
	shell	CY8CPROTO_062_4343W+release	(read only)	6224	6224	0	0.0
			(read/write)	2047472	2047472	0	0.0
			.bss	156732	156732	0	0.0
			.data	4872	4872	0	0.0
			.heap	874840	874840	0	0.0
			.text	1010072	1010072	0	0.0
nrfconnect	lighting-app	nrf52840dk_nrf52840	(read/write)	894699	894699	0	0.0
			bss	113852	113852	0	0.0
			rodata	99676	99676	0	0.0
			text	605624	605624	0	0.0
		nrf52840dk_nrf52840+rpc	(read/write)	858075	858075	0	0.0
			bss	110200	110200	0	0.0
			rodata	91036	91036	0	0.0
			text	580620	580620	0	0.0
		nrf5340dk_nrf5340_cpuapp	(read/write)	820598	820598	0	0.0
			bss	115224	115224	0	0.0
			rodata	94936	94936	0	0.0
			text	535952	535952	0	0.0
	lock-app	nrf52840dk_nrf52840	(read/write)	867283	867283	0	0.0
			bss	111112	111112	0	0.0
			rodata	95796	95796	0	0.0
			text	584996	584996	0	0.0
		nrf5340dk_nrf5340_cpuapp	(read/write)	793434	793434	0	0.0
			bss	112524	112524	0	0.0
			rodata	91084	91084	0	0.0
			text	515416	515416	0	0.0
	pigweed-app	nrf52840dk_nrf52840	(read/write)	497463	497463	0	0.0
			bss	51820	51820	0	0.0
			rodata	45852	45852	0	0.0
			text	339492	339492	0	0.0
	pump-app	nrf52840dk_nrf52840	(read/write)	872019	872019	0	0.0
			bss	111024	111024	0	0.0
			rodata	97148	97148	0	0.0
			text	588396	588396	0	0.0
	pump-controller-app	nrf52840dk_nrf52840	(read/write)	865243	865243	0	0.0
			bss	110904	110904	0	0.0
			rodata	95284	95284	0	0.0
			text	583608	583608	0	0.0
	shell	nrf52840dk_nrf52840	(read/write)	779939	779939	0	0.0
			bss	109696	109696	0	0.0
			rodata	73792	73792	0	0.0
			text	521948	521948	0	0.0
		nrf5340dk_nrf5340_cpuapp	(read/write)	694966	694966	0	0.0
			bss	110680	110680	0	0.0
			rodata	68432	68432	0	0.0
			text	442548	442548	0	0.0
p6	all-clusters-app	default	(read/write)	2352208	2352208	0	0.0
			.bss	110868	110868	0	0.0
			.data	2520	2520	0	0.0
			.heap	919952	919952	0	0.0
			.text	1310472	1310472	0	0.0
	light-app	default	(read/write)	2283256	2283256	0	0.0
			.bss	98632	98632	0	0.0
			.data	2336	2336	0	0.0
			.heap	932376	932376	0	0.0
			.text	1241520	1241520	0	0.0
	lock-app	default	(read/write)	2259424	2259424	0	0.0
			.bss	97512	97512	0	0.0
			.data	2296	2296	0	0.0
			.heap	933536	933536	0	0.0
			.text	1217688	1217688	0	0.0
qpg	lighting-app	qpg6100+debug	(read only)	513300	513300	0	0.0
			(read/write)	122332	122332	0	0.0
			.bss	80360	80360	0	0.0
			.data	964	964	0	0.0
			.text	507980	507980	0	0.0
	lock-app	qpg6100+debug	(read only)	487604	487604	0	0.0
			(read/write)	122336	122336	0	0.0
			.bss	79496	79496	0	0.0
			.data	920	920	0	0.0
			.text	482284	482284	0	0.0
	persistent-storage-app	qpg6100+debug	(read only)	108224	108224	0	0.0
			(read/write)	122332	122332	0	0.0
			.bss	36696	36696	0	0.0
			.data	292	292	0	0.0
			.text	102904	102904	0	0.0
telink	lighting-app	tlsr9518adk80d	(read/write)	798086	798086	0	0.0
			bss	80428	80428	0	0.0
			noinit	37160	37160	0	0.0
			text	557696	557696	0	0.0

[woody-apple]

Fast tracking, given this is updating a test tool.