DecodeException on Map<String, List<String>> result

Hi,

I do have this REST-Resource in my project:

    @GetMapping(ASYNC_MESSAGE + MULTI + KEY_VAR)
    Map<String, List<String>> getNextMessages(@PathVariable(KEY) String[] keys, @RequestParam(LIMIT) Integer limit);

A call on the resources results in an exception:

Sch-Pool4","level":"ERROR","level_value":40000,"stack_trace":"feign.codec.DecodeException: null
\tat feign.InvocationContext.decode(InvocationContext.java:118)
\tat feign.InvocationContext.proceed(InvocationContext.java:88)
\tat feign.ResponseHandler.handleResponse(ResponseHandler.java:63)
\tat feign.SynchronousMethodHandler.executeAndDecode(SynchronousMethodHandler.java:114)
\tat feign.SynchronousMethodHandler.invoke(SynchronousMethodHandler.java:70)
\tat feign.ReflectiveFeign$FeignInvocationHandler.invoke(ReflectiveFeign.java:99)
\tat jdk.proxy3/jdk.proxy3.$Proxy227.getNextMessages(Unknown Source)

If I execute the call manually I get:

{
    "TS_start_queue": []
}

What could be the reason for this? There are no specialites in my environment with spring boot 3.2.7 and spring cloud 2023.0.2.

Start with the declared getNextMessages return type and the JSON response, then trace decoding through feign.InvocationContext.decode, ResponseHandler.handleResponse, and SynchronousMethodHandler.executeAndDecode. A useful outcome is a reproducible explanation of the DecodeException and a regression test or clearly identified missing test case.