diff --git a/spring-graphql-docs/src/docs/asciidoc/index.adoc b/spring-graphql-docs/src/docs/asciidoc/index.adoc
index b3e9348f..efa2b407 100644
--- a/spring-graphql-docs/src/docs/asciidoc/index.adoc
+++ b/spring-graphql-docs/src/docs/asciidoc/index.adoc
@@ -260,6 +260,9 @@ builder.schemaResources(..)
 
 The <<execution.graphqlsource, GraphQlSource section>> explains how to configure that with Spring Boot.
 
+For an example with Apollo Federation, see
+https://github.com/apollographql/federation-jvm-spring-example[federation-jvm-spring-example].
+
 
 [[execution.graphqlsource.schema-traversal]]
 ==== Schema Traversal
diff --git a/spring-graphql/src/test/resources/books/schema.graphqls b/spring-graphql/src/test/resources/books/schema.graphqls
index 0f98f5f6..e1d7bcdd 100644
--- a/spring-graphql/src/test/resources/books/schema.graphqls
+++ b/spring-graphql/src/test/resources/books/schema.graphqls
@@ -1,7 +1,7 @@
 type Query {
     bookById(id: ID): Book
     booksById(id: [ID]): [Book]
-    books(id: ID, name: String, author: String): [Book!]
+    books(id: ID, name: String, author: String): [Book!]!
     booksByCriteria(criteria:BookCriteria): [Book]
     booksByProjectedArguments(name: String, author: String): [Book]
     booksByProjectedCriteria(criteria:BookCriteria): [Book]