when there 's nothing else happening 
(ROOT (SBAR (WHADVP (WRB when)) (S (NP (EX there)) (VP (VBZ 's) (NP (NP (NP (NN nothing)) (JJ else)) (VP (VBG happening)))))))
(ROOT (SBAR (WHADVP (WRB )) (S (NP (EX )) (VP (VBZ ) (NP (NP (NP (NN )) (JJ )) (VP (VBG )))))))