fix:更新已知bug,优化代码

vendor/dasprid/enum/test/NullValueTest.php

@@ -0,0 +1,31 @@
+<?php
+declare(strict_types = 1);
+
+namespace DASPRiD\EnumTest;
+
+use DASPRiD\Enum\Exception\CloneNotSupportedException;
+use DASPRiD\Enum\Exception\SerializeNotSupportedException;
+use DASPRiD\Enum\Exception\UnserializeNotSupportedException;
+use DASPRiD\Enum\NullValue;
+use PHPUnit\Framework\TestCase;
+
+final class NullValueTest extends TestCase
+{
+    public function testExceptionOnCloneAttempt() : void
+    {
+        $this->expectException(CloneNotSupportedException::class);
+        clone NullValue::instance();
+    }
+
+    public function testExceptionOnSerializeAttempt() : void
+    {
+        $this->expectException(SerializeNotSupportedException::class);
+        serialize(NullValue::instance());
+    }
+
+    public function testExceptionOnUnserializeAttempt() : void
+    {
+        $this->expectException(UnserializeNotSupportedException::class);
+        unserialize('O:22:"DASPRiD\\Enum\\NullValue":0:{}');
+    }
+}