An old bug is living in Org.

=C-c C-x C-y= ~org-paste-subtree~ fails just after Emacs start.
Maybe there are more similar issues.

- Start *new* instance of emacs.
- Copy some text that is Org subtree from some
   *external* application (not Emacs).
   I usually come across this issue when I copy capture
   from my Firefox extension. Alternative:
   #+begin_src elisp :results silent
     (require 'ob-shell)
   #+end_src

   #+begin_src bash :results silent
     printf '%b' '* Heading\n\nbody\n' |
       xclip -in -selection clipborad >/dev/null
       # xsel --input --clipboard
   #+end_src

- Try =C-c C-x C-y= or [[elisp:(org-paste-subtree)]]

   + Actual result is the following message:
     : user-error: The kill is not a (set of) tree(s).  Use ‘C-y’ to 
yank anyway
   + Expected result is a heading pasted at the end of the buffer.
   + The result may be achieved by calling [[elisp:(org-paste-subtree)]] 
once more.

- The problem is ~(and kill-ring (current-kill 0))~ expression
   in the definition of ~org-paste-subtree~.
   Restart emacs and repeat steps above skipping ~org-paste-subtree~.
   Notice that ~(current-kill 0)~ call changes value of ~kill-ring~.
   #+begin_src elisp :results pp
     (list (and kill-ring t) (current-kill 0) (and kill-ring t))
   #+end_src

   #+RESULTS:
   : (nil "* Heading\n\nbody\n" t)

I suppose, it is better to let the error from ~current-kill~ to 
propagate (in the case of empty `kill-ring' and clipboard). I do not 
have Windows machine available to test the change.

There is another occurence of ~(and (current-kill 0))~
in ~org-kill-is-subtree-p~. I would rather transform it
to ~org~subtree-p~ to avoid call of ~current-kill~ inside, but this 
patch does not include such change.