Fix: leaked

kernel/excel.c

@@ -566,7 +566,11 @@ PHP_METHOD(vtiful_xls, insertDate)
         type_writer(&_zv_double_time, row, column, &obj->write_ptr, format, obj->format_ptr.format);
     }
 
-    zend_string_release(format);
+    // Release default format
+    if (ZEND_NUM_ARGS() == 3) {
+        zend_string_release(format);
+    }
+
     zval_ptr_dtor(&_zv_double_time);
 }
 /* }}} */