kunit: use NULL macros

Replace the NULL checks with the more specific and idiomatic NULL macros.
Reviewed-by: Brendan Higgins <brendanhiggins@google.com>
Reviewed-by: Daniel Latypov <dlatypov@google.com>
Signed-off-by: Ricardo Ribalda <ribalda@chromium.org>
Signed-off-by: Shuah Khan <skhan@linuxfoundation.org>

lib/kunit/kunit-example-test.c

@@ -91,6 +91,8 @@ static void example_all_expect_macros_test(struct kunit *test)
 	KUNIT_EXPECT_NOT_ERR_OR_NULL(test, test);
 	KUNIT_EXPECT_PTR_EQ(test, NULL, NULL);
 	KUNIT_EXPECT_PTR_NE(test, test, NULL);
+	KUNIT_EXPECT_NULL(test, NULL);
+	KUNIT_EXPECT_NOT_NULL(test, test);
 
 	/* String assertions */
 	KUNIT_EXPECT_STREQ(test, "hi", "hi");

lib/kunit/kunit-test.c

@@ -435,7 +435,7 @@ static void kunit_log_test(struct kunit *test)
 	KUNIT_EXPECT_NOT_ERR_OR_NULL(test,
 				     strstr(suite.log, "along with this."));
 #else
-	KUNIT_EXPECT_PTR_EQ(test, test->log, (char *)NULL);
+	KUNIT_EXPECT_NULL(test, test->log);
 #endif
 }