Full Idea
The paradox of negative existentials says that if 's' does not designate something, then the sentence 's is non-existent' is untrue.
Gist of Idea
's is non-existent' cannot be said if 's' does not designate
Source
C. Anthony Anderson (Identity and Existence in Logic [2014], 2.1)
Book Reference
'Bloomsbury Companion to Philosophical Logic', ed/tr. Horsten,L/Pettigrew,R [Bloomsbury 2014], p.63
A Reaction
This only seems be a problem for logicians. Everyone else can happily say 'my coffee is non-existent'.