src/Shared/Message/Formatter/DefaultFormatter.php
protected function stringize(array &$arguments)
    {
        array_walk($arguments, function (&$value) {
            if (is_object($value)) {
                $value = get_class($value);
            } elseif (is_scalar($value)) {
                $value = (string) $value;
            } else {
                $value = json_encode($value, 0);
            }
        });
        return $this;
    }
protected function stringize(array &$arguments)
    {
        array_walk($arguments, function (&$value) {
            if (is_object($value)) {
                $value = get_class($value);
            } elseif (is_scalar($value)) {
                $value = (string) $value;
            } else {
                $value = json_encode($value, 0);
            }
        });
        return $this;
    }
Convert any non-string item in the arguments to string

@param array &$arguments
@return $this
@access protected
@since  2.0.10 modified to use json_encode