Set opportunity to create enum statically with null value

Author: KartaviK

src/Enum.php

@@ -177,7 +177,7 @@ public static function search($value)
     public static function __callStatic($name, $arguments)
     {
         $array = static::toArray();
-        if (isset($array[$name])) {
+        if (array_key_exists($name, $array)) {
             return new static($array[$name]);
         }
 

tests/EnumTest.php

@@ -262,4 +262,11 @@ public function testJsonSerialize()
         $this->assertJsonStringEqualsJsonString('""',    json_encode(new EnumFixture(EnumFixture::PROBLEMATIC_EMPTY_STRING)));
         $this->assertJsonStringEqualsJsonString('false', json_encode(new EnumFixture(EnumFixture::PROBLEMATIC_BOOLEAN_FALSE)));
     }
+
+    public function testNullableEnum()
+    {
+        $this->assertNull(EnumFixture::PROBLEMATIC_NULL()->getValue());
+        $this->assertNull((new EnumFixture(EnumFixture::PROBLEMATIC_NULL))->getValue());
+        $this->assertNull((new EnumFixture(EnumFixture::PROBLEMATIC_NULL))->jsonSerialize());
+    }
 }