Add nullability annotations to tests in smoke-test/spring-boot-smoke-test-liquibase

See gh-47263

smoke-test/spring-boot-smoke-test-liquibase/build.gradle

@@ -29,3 +29,7 @@ dependencies {
 
 	testImplementation(project(":starter:spring-boot-starter-test"))
 }
+
+tasks.named("compileTestJava") {
+	options.nullability.checking = "tests"
+}

smoke-test/spring-boot-smoke-test-liquibase/src/test/java/smoketest/liquibase/SampleLiquibaseApplicationTests.java

@@ -69,7 +69,10 @@ class SampleLiquibaseApplicationTests {
 		};
 		if (nested.contains(ConnectException.class)) {
 			Throwable root = nested.getRootCause();
-			return root.getMessage().contains("Connection refused");
+			assertThat(root).isNotNull();
+			String message = root.getMessage();
+			assertThat(message).isNotNull();
+			return message.contains("Connection refused");
 		}
 		return false;
 	}