Full Idea
Though someone just beginning to learn English might take it as one, "nobody" is not a singular term, but a quantifier.
Gist of Idea
"Nobody" is not a singular term, but a quantifier
Source
report of Bertrand Russell (On Denoting [1905]) by William Lycan - Philosophy of Language Ch.1
Book Reference
Lycan,William G.: 'Philosophy of Language' [Routledge 2000], p.17
A Reaction
If someone replies to "nobody's there" with "show him to me!", presumably it IS a singular term - just one that doesn't work very well. If you want to get on in life, treat it as a quantifier; if you just want to have fun...