cannot serialize under some circumstances

[eroux]

In https://github.com/OpenPecha/Norbu-Keta-eText-import

I get

  File "/home/admin/Toolkit/openpecha/core/pecha.py", line 334, in save_meta
    dump_yaml(self.meta.dict(exclude_none=True), self.meta_fn)
  File "/home/admin/Toolkit/openpecha/utils.py", line 107, in dump_yaml
    yaml.dump(
  File "/home/admin/pvenv/lib/python3.11/site-packages/yaml/__init__.py", line 253, in dump
    return dump_all([data], stream, Dumper=Dumper, **kwds)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/home/admin/pvenv/lib/python3.11/site-packages/yaml/__init__.py", line 241, in dump_all
    dumper.represent(data)
  File "/home/admin/pvenv/lib/python3.11/site-packages/yaml/representer.py", line 27, in represent
    node = self.represent_data(data)
           ^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/home/admin/pvenv/lib/python3.11/site-packages/yaml/representer.py", line 48, in represent_data
    node = self.yaml_representers[data_types[0]](self, data)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/home/admin/pvenv/lib/python3.11/site-packages/yaml/representer.py", line 207, in represent_dict
    return self.represent_mapping('tag:yaml.org,2002:map', data)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/home/admin/pvenv/lib/python3.11/site-packages/yaml/representer.py", line 118, in represent_mapping
    node_value = self.represent_data(item_value)
                 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/home/admin/pvenv/lib/python3.11/site-packages/yaml/representer.py", line 58, in represent_data
    node = self.yaml_representers[None](self, data)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/home/admin/pvenv/lib/python3.11/site-packages/yaml/representer.py", line 231, in represent_undefined
    raise RepresenterError("cannot represent an object", data)
yaml.representer.RepresenterError: ('cannot represent an object', AnyHttpUrl('https://github.com/OpenPecha/Norbu-Keta-eText-import/blob/main/norbu_ketaka_parser.py', ))