Merge pull request #81 from KartaviK/hotfix/is-valid-key-with-null

Fix validating key with null value

Author: mnapoli

src/Enum.php

@@ -150,7 +150,7 @@ public static function isValidKey($key)
     {
         $array = static::toArray();
 
-        return isset($array[$key]);
+        return isset($array[$key]) || \array_key_exists($key, $array);
     }
 
     /**

tests/EnumTest.php

@@ -190,6 +190,7 @@ public function testIsValidKey()
     {
         $this->assertTrue(EnumFixture::isValidKey('FOO'));
         $this->assertFalse(EnumFixture::isValidKey('BAZ'));
+        $this->assertTrue(EnumFixture::isValidKey('PROBLEMATIC_NULL'));
     }
 
     /**