fixed index not found error in read()

src/Meta.php

@@ -19,7 +19,12 @@ class Meta extends Model
     
     function read( $key ){
         $meta = unserialize( $this->meta );
-        return $meta[ $key ];
+        if ( array_key_exists( $key, $meta ) ){
+            return $meta[ $key ];
+        }
+        else {
+            return null;
+        }
     }
     
     function write( $key, $value ){