feign.Contract.java:
// 137 line
Type[] parameterTypes = ((ParameterizedType) genericType).getActualTypeArguments();

public interface GraphQLClient {
    @RequestMapping(value = "/graphql/d", method = RequestMethod.POST)
    ExecutionResultWrapper execute(@RequestBody QueryWrapper queryWrapper, @RequestHeader HttpHeaders httpHeaders);
}

import own.DefaultFeignConfiguration;
import own.CustomErrorDecoder;
import feign.Client;
import feign.Target;
import feign.hystrix.HystrixFeign;
import feign.slf4j.Slf4jLogger;
import org.springframework.beans.factory.ObjectFactory;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.boot.autoconfigure.http.HttpMessageConverters;
import org.springframework.cloud.netflix.ribbon.SpringClientFactory;
import org.springframework.cloud.openfeign.ribbon.CachingSpringLoadBalancerFactory;
import org.springframework.cloud.openfeign.ribbon.LoadBalancerFeignClient;
import org.springframework.cloud.openfeign.support.ResponseEntityDecoder;
import org.springframework.cloud.openfeign.support.SpringDecoder;
import org.springframework.cloud.openfeign.support.SpringEncoder;
import org.springframework.cloud.openfeign.support.SpringMvcContract;
import org.springframework.stereotype.Component;

@Component
public class ClientBuilder {
    // ...
    public <T> T buildClient(Class<T> targetInterface, String prefix, String url) {
        Target<T> custom = new Target.HardCodedTarget<>(targetInterface, url, prefix + url);
        T target = HystrixFeign.builder()
                .contract(new SpringMvcContract())
                .options(feignConfig.options())
                .logger(new Slf4jLogger())
                .logLevel(feignConfig.level())
                .client(
                        new LoadBalancerFeignClient
                                (new Client.Default(null, null), cachingFactory, clientFactory)
                )
                .decoder(new ResponseEntityDecoder(new SpringDecoder(messageConverters)))
                .encoder(new SpringEncoder(messageConverters))
                .errorDecoder(customErrorDecoder)
                .target(custom); // failed in this method
        return target;
    }
}