AutoCAD Visual LISP / AutoLISP :: Delete Empty Block?

The below gets the block names of empty block records. The blocks may or may not be actually inserted in the dwg. In my case though, apparently they are nested in other blocks in the drawing I am working with... but it looks as if they are part of deeply nested block definitions and therefore cannot be purged.  I checked a couple blocks (the code returns over 1000 in my case) it returns and there are no objects in its definition.

How can I force them out of a drawing - and hopefully reduce it's file size?

(defun NullBlocks (/ block *thisdwg* block nullblocks)
(setq *thisdwg* (vla-get-activedocument (vlax-get-acad-object)))
(vlax-for block (vla-get-blocks *thisdwg*) ;iterate block table
(vla-get-Name block)
(if (= 0 (vla-get-count block))
(setq nullblocks (cons (vla-get-name block) nullblocks))
)
)
nullblocks
)