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

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

@@ -26,6 +26,7 @@ public class SuperBuilderWithCustomBuilderMethod {
 			}
 			@java.lang.SuppressWarnings("all")
 			public 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);
 				return self();