_collections.defaultdict missing __reduce__ builtin

Author: cosminbasca

graalpython/lib-graalpython/_collections.py

@@ -710,3 +710,8 @@ def copy(self):
         for k,v in self.items():
             cp[k] = v
         return cp
+
+    @__graalpython__.builtin_method
+    def __reduce__(self):
+        args = tuple() if self.default_factory is None else (self.default_factory,)
+        return type(self), args, None, None, iter(self.items())