Incorrect handling of falsy literals in SPARQLStore

[eilmiv]

Failing example

from rdflib import Namespace, Graph, Literal
ex = Namespace("https://www.example.org/")
g = Graph("SPARQLStore")
g.open("http://localhost:9999/test/sparql")
print(list(
    g.triples((ex.a, ex.b, Literal("")))
))

... can produce ...

[(rdflib.term.URIRef('https://www.example.org/a'),
  rdflib.term.URIRef('https://www.example.org/b'),
  rdflib.term.Literal('')),
 (rdflib.term.URIRef('https://www.example.org/a'),
  rdflib.term.URIRef('https://www.example.org/b'),
  rdflib.term.URIRef('https://www.example.org/c'))]

... ex:a ex:b ex:c does not match (ex.a, ex.b, Literal(""))
(Literal(""), Literal(0), Literal(False) are treated as a variable)

Solution

These lines should compare to None (a.k.a. ANY) instead:

rdflib/rdflib/plugins/stores/sparqlstore.py

Line 298 in b0392f0

if not o:

rdflib/rdflib/plugins/stores/sparqlstore.py

Line 435 in b0392f0

nts(o if o else Variable("o")),

rdflib/rdflib/plugins/stores/sparqlstore.py

Line 794 in b0392f0

if not obj:

[devkral]

a maybe little off sidenote:

it maybe would be better to use "is None", "is not None" instead of using != == for None comparisons as None is an integer and things can break subtle. For example None == 0 would return True

This should be considered for a proper bugfix and maybe in some other code parts too