plugins leads to error in another plugin

[mmjaeger]

I one of my other plugins I have the following piece of code:
if (isset($post) && 'attachment' == $post->post_type && - this leads to an error like Notice: Undefined property: Eventbrite_Event::$post_type in /Users/Marco/Sites/sites/thinglogix.com/wp-content/plugins/pdfembedder-premium-secure/core/commercial_pdf_embedder.php;

adding $post->post_type = 'post' to the single template fixes the issue?!