assertNull(builder.getContent("content2"));
// content changed
multi1.addContent(multi2);
multi1.addContent(content2);
multi2.addContent(content1);
assertSame(multi1, builder.getContent("multi1"));
assertSame(multi2, builder.getContent("multi2"));
assertSame(content1, builder.getContent("content1"));
assertNull(builder.getContent("content2"));