I've narrowed it down to this so far. If " " changes to "x", there's no problem.
-----------
#!bin/python
import logging
logging.basicConfig(level=logging.DEBUG)
from FuXi.Rete import ReteNetwork
from FuXi.Rete.RuleStore import N3RuleStore
from rdflib import Graph
from rdflib.parser import StringInputSource
ruleStore = N3RuleStore()
ruleGraph = Graph(ruleStore)
n3 = '''
{
?c :p1 ?uri .
} => {
?c :p2 (" " ?uri) .
} .
'''
ruleGraph.parse(StringInputSource(n3), format="n3")
deltaGraph = Graph()
network = ReteNetwork(ruleStore, inferredTarget=deltaGraph)
INFO:rdflib:RDFLib Version: 4.1