throw more descriptive error if no ServiceInstance is found

spring-cloud-netflix-core/src/main/java/org/springframework/cloud/netflix/ribbon/RibbonClientHttpRequestFactory.java

@@ -60,6 +60,9 @@ public class RibbonClientHttpRequestFactory implements ClientHttpRequestFactory
 			throws IOException {
         String serviceId = originalUri.getHost();
         ServiceInstance instance = loadBalancer.choose(serviceId);
+		if (instance == null) {
+			throw new IllegalStateException("No instances available for "+serviceId);
+		}
         URI uri = loadBalancer.reconstructURI(instance, originalUri);
         //@formatter:off
 		IClientConfig clientConfig = clientFactory.getClientConfig(instance.getServiceId());

spring-cloud-netflix-core/src/main/java/org/springframework/cloud/netflix/ribbon/RibbonLoadBalancerClient.java

@@ -23,6 +23,7 @@ import org.springframework.cloud.client.DefaultServiceInstance;
 import org.springframework.cloud.client.ServiceInstance;
 import org.springframework.cloud.client.loadbalancer.LoadBalancerClient;
 import org.springframework.cloud.client.loadbalancer.LoadBalancerRequest;
+import org.springframework.util.Assert;
 import org.springframework.util.ReflectionUtils;
 
 import com.netflix.loadbalancer.ILoadBalancer;
@@ -44,6 +45,7 @@ public class RibbonLoadBalancerClient implements LoadBalancerClient {
 
 	@Override
 	public URI reconstructURI(ServiceInstance instance, URI original) {
+		Assert.notNull(instance, "instance can not be null");
 		String serviceId = instance.getServiceId();
 		RibbonLoadBalancerContext context = this.clientFactory
 				.getLoadBalancerContext(serviceId);