Exception when modified date not set at \Penneo\SDK\Document

[aginev]

sdk-php/src/Document.php

Line 124 in da574d3

return new \Datetime('@'.$this->modified);

Throws exception when modified date is not set. Think it's better to have check similar to

sdk-php/src/SignatureLine.php

Line 83 in da574d3

public function getSignedAt()