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

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

@@ -33,6 +33,8 @@ public class SuperBuilderWithGenericsAndToBuilder {
         return self();
       }
       public @java.lang.SuppressWarnings("all") B items(final java.util.Map<? extends Integer, ? extends String> items) {
+        if ((items == null))
+            throw new java.lang.NullPointerException("items cannot be null");
         if ((this.items$key == null))
             {
               this.items$key = new java.util.ArrayList<Integer>();