Prevent NullPointerException from null context values in ChatClient

Add validation to reject null values in the context map of
ChatClientRequest and ChatClientResponse. This prevents
NullPointerException when advisors use Map.copyOf() to copy
the context, as Map.copyOf() does not allow null values.

- Add null value validation in record constructors
- Add null key and value validation in Builder.context(Map)
- Add null value validation in Builder.context(String, Object)
- Add corresponding tests for all new validations

Closes gh-4952

Author: Nhahan

spring-ai-client-chat/src/main/java/org/springframework/ai/chat/client/ChatClientRequest.java

@@ -37,6 +37,7 @@ public record ChatClientRequest(Prompt prompt, Map<String, Object> context) {
 		Assert.notNull(prompt, "prompt cannot be null");
 		Assert.notNull(context, "context cannot be null");
 		Assert.noNullElements(context.keySet(), "context keys cannot be null");
+		Assert.noNullElements(context.values(), "context values cannot be null");
 	}
 
 	public ChatClientRequest copy() {
@@ -68,12 +69,15 @@ public Builder prompt(Prompt prompt) {
 
 		public Builder context(Map<String, Object> context) {
 			Assert.notNull(context, "context cannot be null");
+			Assert.noNullElements(context.keySet(), "context keys cannot be null");
+			Assert.noNullElements(context.values(), "context values cannot be null");
 			this.context.putAll(context);
 			return this;
 		}
 
 		public Builder context(String key, Object value) {
 			Assert.notNull(key, "key cannot be null");
+			Assert.notNull(value, "value cannot be null");
 			this.context.put(key, value);
 			return this;
 		}

spring-ai-client-chat/src/main/java/org/springframework/ai/chat/client/ChatClientResponse.java

@@ -36,6 +36,7 @@ public record ChatClientResponse(@Nullable ChatResponse chatResponse, Map<String
 	public ChatClientResponse {
 		Assert.notNull(context, "context cannot be null");
 		Assert.noNullElements(context.keySet(), "context keys cannot be null");
+		Assert.noNullElements(context.values(), "context values cannot be null");
 	}
 
 	public ChatClientResponse copy() {
@@ -66,12 +67,15 @@ public Builder chatResponse(@Nullable ChatResponse chatResponse) {
 
 		public Builder context(Map<String, Object> context) {
 			Assert.notNull(context, "context cannot be null");
+			Assert.noNullElements(context.keySet(), "context keys cannot be null");
+			Assert.noNullElements(context.values(), "context values cannot be null");
 			this.context.putAll(context);
 			return this;
 		}
 
 		public Builder context(String key, Object value) {
 			Assert.notNull(key, "key cannot be null");
+			Assert.notNull(value, "value cannot be null");
 			this.context.put(key, value);
 			return this;
 		}

spring-ai-client-chat/src/test/java/org/springframework/ai/chat/client/ChatClientRequestTests.java

@@ -62,6 +62,30 @@ void whenContextHasNullKeysThenThrow() {
 			.hasMessage("context keys cannot be null");
 	}
 
+	@Test
+	void whenContextHasNullValuesThenThrow() {
+		Map<String, Object> context = new HashMap<>();
+		context.put("key", null);
+
+		assertThatThrownBy(() -> new ChatClientRequest(new Prompt(), context))
+			.isInstanceOf(IllegalArgumentException.class)
+			.hasMessage("context values cannot be null");
+
+		assertThatThrownBy(() -> ChatClientRequest.builder().prompt(new Prompt()).context(context).build())
+			.isInstanceOf(IllegalArgumentException.class)
+			.hasMessage("context values cannot be null");
+	}
+
+	@Test
+	void whenBuilderContextMapHasNullKeyThenThrow() {
+		Map<String, Object> context = new HashMap<>();
+		context.put(null, "value");
+
+		assertThatThrownBy(() -> ChatClientRequest.builder().prompt(new Prompt()).context(context).build())
+			.isInstanceOf(IllegalArgumentException.class)
+			.hasMessage("context keys cannot be null");
+	}
+
 	@Test
 	void whenCopyThenImmutableContext() {
 		Map<String, Object> context = new HashMap<>();
@@ -86,6 +110,13 @@ void whenMutateThenImmutableContext() {
 		assertThat(copy.context()).isEqualTo(Map.of("key", "newValue"));
 	}
 
+	@Test
+	void whenBuilderAddsNullValueThenThrow() {
+		assertThatThrownBy(() -> ChatClientRequest.builder().prompt(new Prompt()).context("key", null).build())
+			.isInstanceOf(IllegalArgumentException.class)
+			.hasMessage("value cannot be null");
+	}
+
 	@Test
 	void whenBuilderWithMultipleContextEntriesThenSuccess() {
 		Prompt prompt = new Prompt("test message");

spring-ai-client-chat/src/test/java/org/springframework/ai/chat/client/ChatClientResponseTests.java

@@ -53,6 +53,19 @@ void whenContextHasNullKeysThenThrow() {
 			.hasMessage("context keys cannot be null");
 	}
 
+	@Test
+	void whenContextHasNullValuesThenThrow() {
+		Map<String, Object> context = new HashMap<>();
+		context.put("key", null);
+
+		assertThatThrownBy(() -> new ChatClientResponse(null, context)).isInstanceOf(IllegalArgumentException.class)
+			.hasMessage("context values cannot be null");
+
+		assertThatThrownBy(() -> ChatClientResponse.builder().chatResponse(null).context(context).build())
+			.isInstanceOf(IllegalArgumentException.class)
+			.hasMessage("context values cannot be null");
+	}
+
 	@Test
 	void whenCopyThenImmutableContext() {
 		Map<String, Object> context = new HashMap<>();
@@ -120,16 +133,15 @@ void whenEmptyContextThenCreateSuccessfully() {
 	}
 
 	@Test
-	void whenContextWithNullValuesThenCreateSuccessfully() {
+	void whenContextWithNullValuesThenThrow() {
 		ChatResponse chatResponse = mock(ChatResponse.class);
 		Map<String, Object> context = new HashMap<>();
 		context.put("key1", "value1");
 		context.put("key2", null);
 
-		ChatClientResponse response = new ChatClientResponse(chatResponse, context);
-
-		assertThat(response.context()).containsEntry("key1", "value1");
-		assertThat(response.context()).containsEntry("key2", null);
+		assertThatThrownBy(() -> new ChatClientResponse(chatResponse, context))
+			.isInstanceOf(IllegalArgumentException.class)
+			.hasMessage("context values cannot be null");
 	}
 
 	@Test
@@ -166,6 +178,23 @@ void whenBuilderWithoutChatResponseThenCreateWithNull() {
 		assertThat(response.chatResponse()).isNull();
 	}
 
+	@Test
+	void whenBuilderContextMapHasNullKeyThenThrow() {
+		Map<String, Object> context = new HashMap<>();
+		context.put(null, "value");
+
+		assertThatThrownBy(() -> ChatClientResponse.builder().context(context).build())
+			.isInstanceOf(IllegalArgumentException.class)
+			.hasMessage("context keys cannot be null");
+	}
+
+	@Test
+	void whenBuilderAddsNullValueThenThrow() {
+		assertThatThrownBy(() -> ChatClientResponse.builder().context("key", null).build())
+			.isInstanceOf(IllegalArgumentException.class)
+			.hasMessage("value cannot be null");
+	}
+
 	@Test
 	void whenComplexObjectsInContextThenPreserveCorrectly() {
 		ChatResponse chatResponse = mock(ChatResponse.class);