It’s not a mistake.
1-2	It’s	_	_	_	_	_	_	_	_
1	It	it	PRON	PRP	Case=Nom|Gender=Neut|Number=Sing|Person=3|PronType=Prs	5	nsubj	5:nsubj	Discourse=joint-other_m:118->117:0|Entity=(121-event-giv:inact-cf1-1-ana-War_in_Darfur)
2	’s	be	AUX	VBZ	Mood=Ind|Number=Sing|Person=3|Tense=Pres|VerbForm=Fin	5	cop	5:cop	_
3	not	not	PART	RB	Polarity=Neg	5	advmod	5:advmod	_
4	a	a	DET	DT	Definite=Ind|PronType=Art	5	det	5:det	Bridge=117<127|Entity=(127-event-acc:inf-cf2-2-sgl
5	mistake	mistake	NOUN	NN	Number=Sing	0	root	0:root	Entity=127)|SpaceAfter=No
6	.	.	PUNCT	.	_	5	punct	5:punct	_
