Fix java 8 compatibility issue

Author: oliemansm

.travis.yml

@@ -1,7 +1,7 @@
 language: java
 dist: trusty # https://stackoverflow.com/questions/38912714/travis-failing-junit-tests-for-spring
 jdk:
-  - openjdk8
+  - openjdk11
 before_install:
  - chmod +x travis-build.sh
 script:

graphql-webclient/src/test/java/graphql/kickstart/spring/webclient/boot/GraphQLWebClientTest.java

@@ -83,6 +83,7 @@ void noResponseSucceeds() {
   void listSucceeds() {
     Flux<Simple> response = graphqlClient.flux("query-list.graphql", Simple.class);
     List<Simple> list = response.collectList().block();
+    assertNotNull(list);
     assertEquals(1, list.size());
   }