ToMany collections that are not loaded on freeze are marked unloaded

They are marked as unloaded which means accessing the collection will
throw a PersistenceException.

e.g. customer.getOrders() will throw PersistenceException rather than
return an empty list.

ebean-api/src/main/java/io/ebean/common/BeanList.java

@@ -46,7 +46,8 @@ public final class BeanList<E> extends AbstractBeanCollection<E> implements List
 
   @Override
   public Object freeze() {
-    return list == null ? Collections.emptyList() : Collections.unmodifiableList(list);
+    // null -> illegal to access reference collection
+    return list == null ? null : Collections.unmodifiableList(list);
   }
 
   @Override

ebean-api/src/main/java/io/ebean/common/BeanMap.java

@@ -39,7 +39,8 @@ public final class BeanMap<K, E> extends AbstractBeanCollection<E> implements Ma
 
   @Override
   public Object freeze() {
-    return map == null ? Collections.emptyMap() : Collections.unmodifiableMap(map);
+    // null -> illegal to access reference collection
+    return map == null ? null : Collections.unmodifiableMap(map);
   }
 
   @Override

ebean-api/src/main/java/io/ebean/common/BeanSet.java

@@ -42,7 +42,8 @@ public final class BeanSet<E> extends AbstractBeanCollection<E> implements Set<E
 
   @Override
   public Object freeze() {
-    return set == null ? Collections.emptySet() : Collections.unmodifiableSet(set);
+    // null -> illegal to access reference collection
+    return set == null ? null : Collections.unmodifiableSet(set);
   }
 
   @Override

ebean-core/src/main/java/io/ebeaninternal/server/deploy/BeanPropertyAssocMany.java

@@ -1140,6 +1140,10 @@ public class BeanPropertyAssocMany<T> extends BeanPropertyAssoc<T> implements ST
     if (value instanceof BeanCollection) {
       BeanCollection<?> bc = (BeanCollection<?>) value;
       setValue(entityBean, bc.freeze());
+      if (bc.isReference()) {
+        // make it an error to access the collection (no lazy loading allowed)
+        entityBean._ebean_getIntercept().setPropertyUnloaded(propertyIndex);
+      }
     }
   }
 }

ebean-test/src/test/java/org/tests/query/TestQueryOrderById.java

@@ -42,9 +42,13 @@ public class TestQueryOrderById extends BaseTestCase {
       for (Order order : orders) {
         Customer customer = order.getCustomer();
         if (cachedCustomerIds.contains(customer.getId())) {
-          List<Order> orders1 = customer.getOrders();
-          assertThat(orders1).isEmpty();
-          assertThat(orders1).isSameAs(Collections.EMPTY_LIST);
+          // Illegal to access customer.orders as that was not loaded and no lazy loading is allowed
+          // List<Order> orders1 = customer.getOrders();
+          // assertThat(orders1).isEmpty();
+          // assertThat(orders1).isSameAs(Collections.EMPTY_LIST);
+
+          List<Contact> contacts = customer.getContacts();
+          assertThat(contacts).isNotNull();
 
           // customer.setContacts(new ArrayList<>());
           // customer.setName("modified");
@@ -118,6 +122,7 @@ public class TestQueryOrderById extends BaseTestCase {
 
       // perform some lazy loading if we desire
       for (Customer customer : list) {
+        customer.getContacts().size();
         Address billingAddress = customer.getBillingAddress();
         if (billingAddress != null) {
           Country country = billingAddress.getCountry();