Add nullability annotations to smoke-test/spring-boot-smoke-test-cache

See gh-46587

smoke-test/spring-boot-smoke-test-cache/src/main/java/smoketest/cache/Country.java

@@ -18,6 +18,8 @@ package smoketest.cache;
 
 import java.io.Serializable;
 
+import org.jspecify.annotations.Nullable;
+
 @SuppressWarnings("serial")
 public class Country implements Serializable {
 
@@ -32,7 +34,7 @@ public class Country implements Serializable {
 	}
 
 	@Override
-	public boolean equals(Object o) {
+	public boolean equals(@Nullable Object o) {
 		if (this == o) {
 			return true;
 		}

smoke-test/spring-boot-smoke-test-cache/src/main/java/smoketest/cache/package-info.java

@@ -0,0 +1,20 @@
+/*
+ * Copyright 2012-present the original author or authors.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      https://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+@NullMarked
+package smoketest.cache;
+
+import org.jspecify.annotations.NullMarked;