chore(examples): enable eslint/strict-boolean-expressions and strictNullChecks #1968

Job	Run time
Check version consistency of packages	6s
eslint	2m 13s
Check coding style	14s
setup-and-test (ubuntu-latest, 18.x)	3m 9s
setup-and-test (ubuntu-latest, 20.x)	3m 15s
	8m 57s

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