fixed index not found error in read()

src/Meta.php

@@ -19,8 +19,13 @@ class Meta extends Model
     
     function read( $key ){
         $meta = unserialize( $this->meta );
+        if ( array_key_exists( $key, $meta ) ){
             return $meta[ $key ];
         }
+        else {
+            return null;
+        }
+    }
     
     function write( $key, $value ){
         $meta = unserialize( $this->meta );