fix:更新已知bug,优化代码

vendor/dasprid/enum/src/NullValue.php

@@ -0,0 +1,55 @@
+<?php
+declare(strict_types = 1);
+
+namespace DASPRiD\Enum;
+
+use DASPRiD\Enum\Exception\CloneNotSupportedException;
+use DASPRiD\Enum\Exception\SerializeNotSupportedException;
+use DASPRiD\Enum\Exception\UnserializeNotSupportedException;
+
+final class NullValue
+{
+    /**
+     * @var self
+     */
+    private static $instance;
+
+    private function __construct()
+    {
+    }
+
+    public static function instance() : self
+    {
+        return self::$instance ?: self::$instance = new self();
+    }
+
+    /**
+     * Forbid cloning enums.
+     *
+     * @throws CloneNotSupportedException
+     */
+    final public function __clone()
+    {
+        throw new CloneNotSupportedException();
+    }
+
+    /**
+     * Forbid serializing enums.
+     *
+     * @throws SerializeNotSupportedException
+     */
+    final public function __sleep() : array
+    {
+        throw new SerializeNotSupportedException();
+    }
+
+    /**
+     * Forbid unserializing enums.
+     *
+     * @throws UnserializeNotSupportedException
+     */
+    final public function __wakeup() : void
+    {
+        throw new UnserializeNotSupportedException();
+    }
+}