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NullPointerException in McpClientSession #605
Description
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Bug description
In enola-dev/enola#1862, I've run into:
java.lang.NullPointerException: data
at java.base/java.util.Objects.requireNonNull(Objects.java:259)
at reactor.core.publisher.FluxHandle$HandleSubscriber.next(FluxHandle.java:251)
at io.modelcontextprotocol.spec.McpClientSession.lambda$sendRequest$12(McpClientSession.java:280)
at reactor.core.publisher.FluxHandle$HandleSubscriber.onNext(FluxHandle.java:113)
at reactor.core.publisher.SerializedSubscriber.onNext(SerializedSubscriber.java:99)
at reactor.core.publisher.FluxTimeout$TimeoutMainSubscriber.onNext(FluxTimeout.java:181)
at reactor.core.publisher.MonoCreate$DefaultMonoSink.success(MonoCreate.java:176)
I guess that this means that this is null?
Environment
0.14.1
Steps to reproduce
Unfortunately I'm unable to reproduce it locally even myself, but I am consistently seeing this on a failing CI build.
Expected behavior
Clear error message instead of NPE.
Minimal Complete Reproducible example
N/A
Activity
vorburger commentedon Nov 8, 2025
FTR: I'm still seeing this NPE after upgrading from
0.14.1to0.15.0. I'll try to debug it using #607. @tzolovdeps: Use MCP lib from vorburger fork (to test un-merged changes; re. e…
deps: Use MCP lib from vorburger fork (to test un-merged changes; re. e…
vorburger commentedon Nov 8, 2025
Running my enola-dev/enola#1862 with #607 I get:
So it look like there appear to be some cases when that
jsonRpcResponseis not itself null, but has neither aresultnor anerror, which I guess is surprising? Perhaps that should be caught earlier?deps: Use MCP lib from vorburger fork (to test un-merged changes; re. e…
vorburger commentedon Nov 8, 2025
In my case, this happened because I used my own custom Jackson ObjectMapper.
enola-dev/enola#1904 works around this in my project ("downstream"). But it would probably be good if this library wouldn't just throw a confusing internal NPE, but would catch this problem more clearly and earlier. I'll see if I contribute to that.
fix: Validate JSONRPCResponse in constructor (fixes modelcontextproto…
vorburger commentedon Nov 9, 2025
#658 proposed for this.