@FeignClient from openfeign and Observable leads to fasterxml.jackson.databind.exc.InvalidDefinitionException

Question

I've a project with the following feign client

@FeignClient(name = "name", url = "${tokenService}")
public interface TokenService {
    @RequestMapping(path = "/SLJsonWebTokenWrapper/token/wrap", method = RequestMethod.POST,
        consumes = MediaType.APPLICATION_JSON_VALUE, produces = MediaType.APPLICATION_JSON_VALUE)
    Observable<Token> getToken(@RequestHeader("externalSystemCode") String systemCode,
                           @RequestBody TokenRequest tokenRequest);
}

and the following dependency

org.springframework.cloud:spring-cloud-starter-feign

Everyting works fine. When I update my project to Spring Boot 2 (and use org.springframework.cloud:spring-cloud-starter-openfeign) requests to this service fail with exception

c.f.j.d.e.InvalidDefinitionException: Cannot construct instance of 
`rx.Observable` (no Creators, like default construct, exist): cannot 
deserialize from Object value (no delegate- or property-based Creator)
 at [Source: (ByteArrayInputStream); line: 1, column: 2]
at c.f.j.d.e.InvalidDefinitionException.from(InvalidDefinitionException.java:67)
at c.f.j.d.DeserializationContext.reportBadDefinition(DeserializationContext.java:1452)
at c.f.j.d.DeserializationContext.handleMissingInstantiator(DeserializationContext.java:1028)
at c.f.j.d.d.BeanDeserializerBase.deserializeFromObjectUsingNonDefault(BeanDeserializerBase.java:1297)
at c.f.j.d.d.BeanDeserializer.deserializeFromObject(BeanDeserializer.java:326)
at c.f.j.d.d.BeanDeserializer.deserialize(BeanDeserializer.java:159)
at c.f.j.d.ObjectMapper._readMapAndClose(ObjectMapper.java:4013)
at c.f.j.d.ObjectMapper.readValue(ObjectMapper.java:3084)
... 1 frames excluded
... 99 common frames omitted
Wrapped by: o.s.h.c.HttpMessageConversionException: Type definition 
error: [simple type, class rx.Observable]; nested exception is 
com.fasterxml.jackson.databind.exc.InvalidDefinitionException: Cannot 
construct instance of `rx.Observable` (no Creators, like default 
construct, exist): cannot deserialize from Object value (no delegate- 
or property-based Creator)
at [Source: (ByteArrayInputStream); line: 1, column: 2]
at o.s.h.c.j.AbstractJackson2HttpMessageConverter.readJavaType(AbstractJackson2HttpMessageConverter.java:240)
at o.s.h.c.j.AbstractJackson2HttpMessageConverter.read(AbstractJackson2HttpMessageConverter.java:225)
... 3 frames excluded
at f.o.OptionalDecoder.decode(OptionalDecoder.java:36)
at f.SynchronousMethodHandler.decode(SynchronousMethodHandler.java:170)
... 93 common frames omitted
Wrapped by: f.c.DecodeException: Type definition error: [simple type, class rx.Observable]; nested exception is com.fasterxml.jackson.databind.exc.InvalidDefinitionException: Cannot construct instance of `rx.Observable` (no Creators, like default construct, exist): cannot deserialize from Object value (no delegate- or property-based Creator)
 at [Source: (ByteArrayInputStream); line: 1, column: 2]

How can I fix it?

P.S. This question is similar to Spring cloud netflix and HystrixObservable --> JsonMappingException, that has no answer though

Answer 1

Adding this option fixed my problem

feign.hystrix.enabled: true