Fix missing entity types for type reference resolution (#520)

Author: igdianov

schema/src/main/java/com/introproventures/graphql/jpa/query/schema/impl/GraphQLJpaSchemaBuilder.java

@@ -82,6 +82,7 @@
 import java.util.concurrent.ConcurrentHashMap;
 import java.util.concurrent.atomic.AtomicInteger;
 import java.util.function.Function;
+import java.util.function.Predicate;
 import java.util.function.Supplier;
 import java.util.stream.Collectors;
 import java.util.stream.Stream;
@@ -184,6 +185,13 @@ public GraphQLSchema build() {
 
         GraphQLSchema.Builder schema = GraphQLSchema.newSchema().query(getQueryType());
 
+        entityManager
+            .getMetamodel()
+            .getEntities()
+            .stream()
+            .filter(Predicate.not(entityCache::containsKey))
+            .forEach(entity -> schema.additionalType(getEntityObjectType(entity)));
+
         if (enableSubscription) {
             schema.subscription(getSubscriptionType());
         }