To count Null values when using the other aggregate functions, use the Nz function, which converts Null values to zeroes so they are included in a calculation.
1	To	to	PART	_	_	2	mark	_	_
2	count	count	VERB	INF	VerbForm=Inf	12	advcl	_	_
3	Null	null	NOUN	SG-NOM	Number=Sing	4	compound	_	_
4	values	value	NOUN	PL-NOM	Number=Plur	2	obj	_	_
5	when	when	SCONJ	_	Case=Nom	6	mark	_	_
6	using	use	VERB	ING	Tense=Pres|VerbForm=Part	2	advcl	_	_
7	the	the	DET	DEF	Definite=Def|PronType=Art	8	det	_	_
8	other	other	ADJ	POS	Degree=Pos	10	amod	_	_
9	aggregate	aggregate	NOUN	SG-NOM	Number=Sing	10	compound	_	_
10	functions	function	NOUN	PL-NOM	Number=Plur	6	obj	_	SpaceAfter=No
11	,	,	PUNCT	Comma	_	2	punct	_	_
12	use	use	VERB	IMP	Mood=Imp|VerbForm=Fin	0	root	_	_
13	the	the	DET	DEF	Definite=Def|PronType=Art	15	det	_	_
14	Nz	Nz	PROPN	SG-NOM	Number=Sing	15	compound	_	_
15	function	function	NOUN	SG-NOM	Number=Sing	12	obj	_	SpaceAfter=No
16	,	,	PUNCT	Comma	_	18	punct	_	_
17	which	which	PRON	WH-REL	PronType=Rel	18	nsubj	_	_
18	converts	convert	VERB	PRES	Mood=Ind|Number=Sing|Person=3|Tense=Pres|VerbForm=Fin	15	acl:relcl	_	_
19	Null	null	NOUN	SG-NOM	Number=Sing	20	compound	_	_
20	values	value	NOUN	PL-NOM	Number=Plur	18	obj	_	_
21	to	to	ADP	_	_	22	case	_	_
22	zeroes	zero	NOUN	PL-NOM	Number=Plur	20	nmod	_	_
23	so	so	SCONJ	_	_	26	mark	_	_
24	they	they	PRON	PERS-PL-NOM	Case=Nom|Number=Plur|Person=3|PronType=Prs	26	nsubj:pass	_	_
25	are	be	AUX	PRES-AUX	Mood=Ind|Tense=Pres|VerbForm=Fin	26	aux:pass	_	_
26	included	include	VERB	PASS	Tense=Past|VerbForm=Part|Voice=Pass	20	advcl	_	_
27	in	in	ADP	_	_	29	case	_	_
28	a	a	DET	IND-SG	Definite=Ind|PronType=Art	29	det	_	_
29	calculation	calculation	NOUN	SG-NOM	Number=Sing	26	obl	_	SpaceAfter=No
30	.	.	PUNCT	Period	_	12	punct	_	_
