fix: Avoid NPE in McpClientSession

vorburger · vorburger · commit c49241c85496 · 2025-11-08T21:08:13.000+01:00
diff --git a/mcp-core/src/main/java/io/modelcontextprotocol/spec/McpClientSession.java b/mcp-core/src/main/java/io/modelcontextprotocol/spec/McpClientSession.java
@@ -283,7 +283,15 @@ public <T> Mono<T> sendRequest(String method, Object requestParams, TypeRef<T> t
 					deliveredResponseSink.complete();
 				}
 				else {
-					deliveredResponseSink.next(this.transport.unmarshalFrom(jsonRpcResponse.result(), typeRef));
+					var result = jsonRpcResponse.result();
+					var unmarshalled = this.transport.unmarshalFrom(result, typeRef);
+					// https://github.com/modelcontextprotocol/java-sdk/issues/605
+					if (unmarshalled != null)
+						deliveredResponseSink.next(unmarshalled);
+					else
+						// NB: next() cannot be called with null
+						deliveredResponseSink
+							.error(new IllegalStateException("Failed to unmarshal response: " + jsonRpcResponse));
 				}
 			}
 		});

Original file line number	Diff line number	Diff line change
`@@ -283,7 +283,15 @@ public <T> Mono<T> sendRequest(String method, Object requestParams, TypeRef<T> t`
`283`	`283`	`deliveredResponseSink.complete();`
`284`	`284`	`}`
`285`	`285`	`else {`
`286`		`- deliveredResponseSink.next(this.transport.unmarshalFrom(jsonRpcResponse.result(), typeRef));`
	`286`	`+ var result = jsonRpcResponse.result();`
	`287`	`+ var unmarshalled = this.transport.unmarshalFrom(result, typeRef);`
	`288`	`+ // https://github.com/modelcontextprotocol/java-sdk/issues/605`
	`289`	`+ if (unmarshalled != null)`
	`290`	`+ deliveredResponseSink.next(unmarshalled);`
	`291`	`+ else`
	`292`	`+ // NB: next() cannot be called with null`
	`293`	`+ deliveredResponseSink`
	`294`	`+ .error(new IllegalStateException("Failed to unmarshal response: " + jsonRpcResponse));`
`287`	`295`	`}`
`288`	`296`	`}`
`289`	`297`	`});`