what wrong with java lambda :: expression ? why ? what diff between :: and normal expression?

public static void main(String[] args) {
    Manager manager1 = new Manager();
    Manager manager2 = null;

    // both line 1 and line 2 are ok
    NullUtils.objectNullFieldNull(manager1, () -> manager1.getName(), "");
    NullUtils.objectNullFieldNull(manager1, manager1::getName, "");

    // line 1 is ok but line 2 will throw NullPointerException
    NullUtils.objectNullFieldNull(manager2, () -> manager2.getName(), "");
    NullUtils.objectNullFieldNull(manager2, manager2::getName, "");
}

As we know, we can use xxx::yyy instead of () -> xxx.yyy() in Java, but if xxx is null, they will be different.

The version with :: will throw a NullPointerException, but () -> xxx.yyy() not throw an exception until the function is actually called.

Why is this?

I use IntelliJ IDEA to code, and if the code can use :: instead of ->, then the IDE will show a warning, telling me to change it to use :: (even though that would cause a NullPointerException).

How do I resolve this?

Other related code:

public class NullUtils {

    public static <O, R> R objectNullFieldNull(O o, Supplier<R> supplier, R orv) {
        return Objects.isNull(o) ? orv : objectNull(supplier.get(), orv);
    }

    public static <O> O objectNull(O original, O target) {
        return Objects.isNull(original) ? target : original;
    }
}

@Data
@Builder(toBuilder = true)
@NoArgsConstructor
@AllArgsConstructor
public class Manager {

    private String code;

    private String name;

    private String mobile;
}