What this does is allow the developer to control how nulls are treated by default for stateless updates (when you don't explicitly specify which properties are to be updated).

/**
	 * Force an update additionally specifying whether to
	 * 'deleteMissingChildren' when the update cascades to a OneToMany or
	 * ManyToMany.
	 * <p>
	 * By default the deleteMissingChildren is true and it is assumed that when
	 * cascade saving a O2M or M2M relationship that the relationship is 'fully
	 * loaded' and any child beans that are no longer on the relationship will
	 * be deleted.
	 * </p>
	 * <p>
	 * You can use this method to FORCE an update to occur (even on a bean that
	 * has not been fetched but say built from JSON or XML). When
	 * {@link EbeanServer#save(Object)} is used Ebean determines whether to use
	 * an insert or an update based on the state of the bean. Using this method
	 * will force an update to occur.
	 * </p>
	 * <p>
	 * It is expected that this method is most useful in stateless REST services
	 * or web applications where you have the values you wish to update but no
	 * existing bean.
	 * </p>
	 * 
	 * @param bean
	 *            the bean to update
	 * @param updateProps
	 *            optionally you can specify the properties to update (can be
	 *            null).
	 * @param t
	 *            optionally you can specify the transaction to use (can be
	 *            null).
	 * @param deleteMissingChildren
	 *            specify false if you do not want 'missing children' of a
	 *            OneToMany or ManyToMany to be automatically deleted.
	 * @param updateNullProperties
	 *            specify true if by default you want properties with null
	 *            values to be included in the update and false if those
	 *            properties should be treated as 'unloaded' and excluded from
	 *            the update. This only takes effect if the updateProps is null.
	 */
	public void update(Object bean, Set<String> updateProps, Transaction t, boolean deleteMissingChildren, boolean updateNullProperties);