fixing MyPy errors

rdflib/plugins/parsers/hext.py

@@ -27,7 +27,14 @@ def _load_json_line(self, line: str):
         return [x if x != "" else None for x in json.loads(line)]
 
     def _parse_hextuple(self, cg: ConjunctiveGraph, tup: List[Union[str, None]]):
+        # all values check
+        # subject, predicate, value, datatype cannot be None
+        # language and graph may be None
+        if tup[0] is None or tup[1] is None or tup[2] is None or tup[3] is None:
+            raise ValueError("subject, predicate, value, datatype cannot be None")
+
         # 1 - subject
+        s: Union[URIRef, BNode]
         if tup[0].startswith("_"):
             s = BNode(value=tup[0].replace("_:", ""))
         else:
@@ -37,6 +44,7 @@ def _parse_hextuple(self, cg: ConjunctiveGraph, tup: List[Union[str, None]]):
         p = URIRef(tup[1])
 
         # 3 - value
+        o: Union[URIRef, BNode, Literal]
         if tup[3] == "globalId":
             o = URIRef(tup[2])
         elif tup[3] == "localId":

rdflib/plugins/serializers/hext.py

@@ -19,7 +19,7 @@ class HextuplesSerializer(Serializer):
 
     def __init__(self, store: Union[Graph, ConjunctiveGraph]):
         self.default_context: Optional[Node]
-        if type(store) != Graph:
+        if isinstance(store, ConjunctiveGraph):
             self.contexts = list(store.contexts())
             if store.default_context:
                 self.default_context = store.default_context