Empty book object - possibly because of nonexistent NID

Hi,

this module would cover my needs perfectly (separated block for each book, visible block in non-book pages), but it generates a warning (and a notice) which annoys me a lot. They can be hidden but it would be great to get rid of them. I have these logs:
Warning: Creating default object from empty value in bookblock_block_view() (line 65 of /.../sites/all/modules/bookblock/bookblock.module).
Notice: Undefined property: stdClass::$nid in node_access() function

They appeare in every book pages but interestingly don't in a non-book page. I browsed through the queries and found an interesting one: SELECT n.nid, n.uid, n.status, n.type FROM node n WHERE n.nid = '3338'. This is generated in bookblock_block_view() function (line 63). It's very odd because there isn't any node where nid=3338. I don't really understand how it's possible. $delta argument gets this value from somwhere but I couldn't figure out from where.

Hopefully somebody can help me.