Update ResponseSubscribers.java

sink.must() must be executed, otherwise in the case of empty return (such as notify), the deliveredSink of sendMessage will not be able to process the stream correctly, resulting in Client failed to initialize by explicit API call

Author: codezkk

mcp/src/main/java/io/modelcontextprotocol/client/transport/ResponseSubscribers.java

@@ -237,10 +237,10 @@ protected void hookOnNext(String line) {
 
 		@Override
 		protected void hookOnComplete() {
-			if (this.eventBuilder.length() > 0) {
-				String data = this.eventBuilder.toString();
-				this.sink.next(new AggregateResponseEvent(responseInfo, data));
-			}
+			// sink.next() is must 
+			String data = this.eventBuilder.toString();
+			this.sink.next(new AggregateResponseEvent(responseInfo, data));
+		
 			this.sink.complete();
 		}