function _dozent_get_course( $post = null ) {

		if ( $post instanceof \Dozent\Course ){
			return $post;
		}

		$post = get_post( $post );

		if ( $post->post_type === 'dozent_course' ){
			return $post;
		}

		if ( $post->post_type === 'dozent_lecture' || $post->post_type === 'dozent_quiz'
		     || $post->post_type === 'dozent_assignment' ) {

			$course_id = dozent_get_course_id_by_content( $post );

			return get_post( $course_id );
		}

		return null;

	}