get_fragment() will raise a KeyError if the fragment is not found, not return a falsey value.

Author: jhgg

graphql/core/validation/__init__.py

@@ -68,9 +68,13 @@ def enter(self, node, key, parent, path, ancestors):
             result = False
 
         if result is None and getattr(self.instance, 'visit_spread_fragments', False) and isinstance(node, FragmentSpread):
-            fragment = self.instance.context.get_fragment(node.name.value)
-            if fragment:
-                visit(fragment, self)
+            try:
+                fragment = self.instance.context.get_fragment(node.name.value)
+            except KeyError:
+                pass
+            else:
+                if fragment:
+                    visit(fragment, self)
 
         if result is False:
             self.type_info.leave(node)