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