# Null handling: IGNORE vs the default on a patch, and RETURN_DEFAULT on whole objects and collections


--- patch(): nullValuePropertyMappingStrategy = IGNORE, applied with a patch whose components are all null ---
before: email=Asha.Mehta@Example.com, nickname=ash, roles=[USER], address=12 Park Road/Pune/411001
after : email=Asha.Mehta@Example.com, nickname=ash, roles=[USER], address=12 Park Road/Pune/411001

--- replace(): the default strategy (SET_TO_NULL), same all-null patch ---
before: email=Asha.Mehta@Example.com, nickname=ash, roles=[USER], address=12 Park Road/Pune/411001
after : email=null, nickname=null, roles=null, address=null

--- whole objects and collections: OrderMapper (default) vs LenientOrderMapper (RETURN_DEFAULT) ---
strict.toDto(null)          : null
lenient.toDto(null)         : OrderDto[id=null, status=null, placedAt=null, lines=null, total=null]
strict  order, lines = null : lines=null
lenient order, lines = null : lines=[]
strict.toDtos(null)         : null

--- the generated patch() (IGNORE): every assignment is guarded ---
    public void patch(CustomerPatch patch, Customer customer) {
        if ( patch == null ) {
            return;
        }

        if ( patch.email() != null ) {
            customer.setEmail( patch.email() );
        }
        if ( patch.nickname() != null ) {
            customer.setNickname( patch.nickname() );
        }
        if ( patch.address() != null ) {
            if ( customer.getAddress() == null ) {
                customer.setAddress( new Address() );
            }
            addressMapper.update( patch.address(), customer.getAddress() );
        }
        if ( customer.getRoles() != null ) {
            Set<String> set = patch.roles();
            if ( set != null ) {
                customer.getRoles().clear();
                customer.getRoles().addAll( set );
            }
        }
        else {
            Set<String> set = patch.roles();
            if ( set != null ) {
                customer.setRoles( new LinkedHashSet<String>( set ) );
            }
        }
    }