Fix TopicPartitionOffset Hash Code (NPE)

**cherry-pick to all supported**

Author: garyrussell

spring-kafka/src/main/java/org/springframework/kafka/support/TopicPartitionOffset.java

@@ -213,7 +213,7 @@ public boolean equals(Object o) {
 
 	@Override
 	public int hashCode() {
-		return this.topicPartition.hashCode() + this.position.hashCode();
+		return Objects.hash(this.topicPartition, this.position);
 	}
 
 	@Override

spring-kafka/src/test/java/org/springframework/kafka/support/TopicPartitionOffsetTests.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2020 the original author or authors.
+ * Copyright 2020-2022 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.
@@ -18,6 +18,9 @@
 
 import static org.assertj.core.api.Assertions.assertThat;
 
+import java.util.Objects;
+
+import org.apache.kafka.common.TopicPartition;
 import org.junit.jupiter.api.Test;
 
 import org.springframework.kafka.support.TopicPartitionOffset.SeekPosition;
@@ -35,4 +38,10 @@ void hashCodeTest() {
 				.isNotEqualTo(new TopicPartitionOffset("foo",  1, SeekPosition.END).hashCode());
 	}
 
+	@Test
+	void hashCodeNPE() {
+		assertThat(new TopicPartitionOffset("foo", 0).hashCode())
+				.isEqualTo(Objects.hash(new TopicPartition("foo", 0), null));
+	}
+
 }