[singular][issue #2221] the plural builder method now nullchecks its argument with configurable results.

test/transform/resource/after-ecj/SuperBuilderWithCustomBuilderMethod.java

@@ -20,6 +20,8 @@ public class SuperBuilderWithCustomBuilderMethod {
         return self();
       }
       public @java.lang.SuppressWarnings("all") B items(final java.util.Collection<? extends String> items) {
+        if ((items == null))
+            throw new java.lang.NullPointerException("items cannot be null");
         if ((this.items == null))
             this.items = new java.util.ArrayList<String>();
         this.items.addAll(items);