ChatClient advisors NPE when context contains null values

[Nhahan]

Bug description

ChatClientRequest only forbids null keys, not null values. The advisors (ChatModelStreamAdvisor, ChatModelCallAdvisor, SafeGuardAdvisor) call Map.copyOf(request.context()), and that blows up with NullPointerException if any value is null. The call/stream fails before the model is invoked.

Environment

• Spring AI: main (latest)
• Java: 17 (also seen on 21)
• Vector store: not involved

Steps to reproduce

1. Build a ChatClientRequest with a null context value, e.g. context("tenantId", null).
2. Use a ChatClient with default advisors (or directly use ChatModelStreamAdvisor/ChatModelCallAdvisor).
3. Call .stream(...) or .call(...).
4. Map.copyOf throws NPE inside the advisor.

Expected behavior

Either reject the request up front with a clear validation error, or avoid throwing NPE in the advisors when context contains null values.

Minimal complete reproducible example

import static org.assertj.core.api.Assertions.assertThatThrownBy;

import org.junit.jupiter.api.Test;
import org.springframework.ai.chat.client.ChatClientRequest;
import org.springframework.ai.chat.prompt.Prompt;

class ChatClientRequestNullContextTests {

    @Test
    void nullContextValueTriggersNpeInAdvisor() {
        ChatClientRequest request = ChatClientRequest.builder()
            .prompt(new Prompt("hi"))
            .context("tenantId", null) // null value
            .build();

        // Same failure point as in the advisors:
        assertThatThrownBy(() -> java.util.Map.copyOf(request.context()))
            .isInstanceOf(NullPointerException.class);
    }
}

Affected code

• spring-ai-client-chat/src/main/java/org/springframework/ai/chat/client/advisor/ChatModelStreamAdvisor.java
• spring-ai-client-chat/src/main/java/org/springframework/ai/chat/client/advisor/ChatModelCallAdvisor.java
• spring-ai-client-chat/src/main/java/org/springframework/ai/chat/client/advisor/SafeGuardAdvisor.java
• spring-ai-client-chat/src/main/java/org/springframework/ai/chat/client/ChatClientRequest.java

Proposed resolution

Tighten ChatClientRequest validation to disallow null values in context, so invalid requests fail fast with a clear message, and the advisors can keep their immutable Map.copyOf calls.

[ThomasVitale]

Thanks for reporting this issue! I wonder if we should lean towards allowing null values. I'm trying to think of cases where that might happen intentionally. For example, a tenantId might be null if a certain request happens outside the tenant context (e.g. some background job). Another example is that we set some default context when building the ChatClient instance, and we want to "remove" one of the parameters by setting it to null in one specific usage.

So perhaps I would consider changing the way the Map is copied (which is done to ensure we never mutate the original Map).

If we go with new HashMap<>(request.content) instead of Map.copyOf(request.context()), no NPE should be thrown when a value is null.

What do you think?