uninitialized_zval在PHP内核中起什么作用？

Question

uninitialized_zval出现在PHP内核的多个位置，但我不知道它的作用。例如，在ZEND_ASSIGN_DIM_SPEC_CV_UNUSED_OP_DATA_CONST_HANDLER处理程序中：

@Entity
@Table(name="place")
public class Place {

    @Id
    @GeneratedValue(generator = "UUID")
    @GenericGenerator(
        name = "UUID",
        strategy = "org.hibernate.id.UUIDGenerator"
    )
    @org.hibernate.annotations.Type(type="uuid-char")
    private UUID id;

    private String name;
    private String subLocality;
    private String locality;
    private String postalCode;
    private String administrativeArea;
    private String country;
    private Double latitude;
    private Double longitude;

    private Double rating;
    private Long reviewCount;

    @OneToMany(mappedBy="place",cascade=CascadeType.PERSIST,fetch=FetchType.EAGER)
    private Set<PlaceImage> placeImages = new LinkedHashSet<>();

为什么使用uninitialized_zval？何时使用uninitialized_zval？