set empty value by default

src/Interface/Model/Pool.php

@@ -20,7 +20,7 @@ interface Pool
 
     public function set(
         string $key,
-        string $value,
+        string $value = '',
         string $flags = 'c',
         int $offset = 0,
         int $mode = 0644,

src/Model/Pool.php

@@ -40,7 +40,7 @@ class Pool implements \Yggverse\Yoda\Interface\Model\Pool
 
     public function set(
         string $key,
-        string $value,
+        string $value = '',
         string $flags = 'c',
         int $offset = 0,
         int $mode = 0644,