Enable strict null checking for String test (#65449)

src/tsconfig.strictNullChecks.json

@@ -145,6 +145,7 @@
 		"./vs/base/test/common/paths.test.ts",
 		"./vs/base/test/common/resources.test.ts",
 		"./vs/base/test/common/scrollable.test.ts",
+		"./vs/base/test/common/strings.test.ts",
 		"./vs/base/test/common/types.test.ts",
 		"./vs/base/test/common/utils.ts",
 		"./vs/base/test/common/uuid.test.ts",

src/vs/base/test/common/strings.test.ts

@@ -320,7 +320,7 @@ suite('Strings', () => {
 	});
 
 	test('fuzzyContains', () => {
-		assert.ok(!strings.fuzzyContains(void 0, null));
+		assert.ok(!strings.fuzzyContains((void 0)!, null!));
 		assert.ok(strings.fuzzyContains('hello world', 'h'));
 		assert.ok(!strings.fuzzyContains('hello world', 'q'));
 		assert.ok(strings.fuzzyContains('hello world', 'hw'));