Fix when json/jackson bean inserted as null and not changed

Expectation is that it is not included in update (still null, no change)

ebean-core/src/test/java/org/tests/model/json/TestJacksonPlainBean.java

@@ -10,6 +10,31 @@ import static org.assertj.core.api.Assertions.assertThat;
 
 public class TestJacksonPlainBean {
 
+  @Test
+  public void insertNullStayNull() {
+
+    // insert with jackson beans as null
+    EBasicPlain bean = new EBasicPlain();
+    bean.setAttr("n0");
+    DB.save(bean);
+
+    LoggedSqlCollector.start();
+    bean.setAttr("n1");
+    DB.save(bean);
+    expectedSql(0, "update ebasic_plain set attr=?, version=? where id=? and version=?");
+
+    bean.setPlainBean(new PlainBean("x", 1));
+    DB.save(bean);
+    expectedSql(0, "update ebasic_plain set plain_bean=?, version=? where id=? and version=?");
+
+    final EBasicPlain found = DB.find(EBasicPlain.class, bean.getId());
+    found.setAttr("n2");
+    DB.save(found);
+    expectedSql(1, "update ebasic_plain set attr=?, version=? where id=? and version=?");
+
+    LoggedSqlCollector.stop();
+  }
+
   @Test
   public void insertUpdate() {