add nullable values support

src/Interface/Model/Pool.php

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

src/Model/Pool.php

@@ -24,29 +24,38 @@ class Pool implements \Yggverse\Yoda\Interface\Model\Pool
         int $count = 0
     ): ?string
     {
-        if (isset($this->_data[$key]))
+        if (empty($this->_data[$key]))
         {
-            return shmop_read(
+            return null;
-                $this->_data[$key],
-                $start,
-                $count ? $count : shmop_size(
-                    $this->_data[$key]
-                )
-            );
         }
 
-        return null;
+        return shmop_read(
+            $this->_data[$key],
+            $start,
+            $count ? $count : shmop_size(
+                $this->_data[$key]
+            )
+        );
     }
 
     public function set(
         string $key,
-        string $value = '',
+        ?string $value = null,
         string $flags = 'c',
         int $offset = 0,
         int $mode = 0644,
         ?string $encoding = null
     ): int
     {
+        if (empty($value))
+        {
+            // @TODO delete from memory
+
+            $this->_data[$key] = null;
+
+            return 0;
+        }
+
         if ($this->_data[$key] = shmop_open(crc32($this->_namespace . $key), $flags, $mode, mb_strlen($value, $encoding)))
         {
             return shmop_write(
@@ -63,9 +72,12 @@ class Pool implements \Yggverse\Yoda\Interface\Model\Pool
     {
         foreach ($this->_data as $data)
         {
-            shmop_delete(
+            if ($data)
-                $data
+            {
-            );
+                shmop_delete(
+                    $data
+                );
+            }
         }
 
         $this->_data = [];