TypeError: '<' not supported between instances of 'NoneType' and 'String'

classifier_sorting.py

import copy

import tomlkit


toml = """
a=[
  # foo,
  "abc"
]
"""

doc = tomlkit.parse(toml)
array = doc["a"]
print(set(array))
array = copy.copy(array)
array = set(array)
print(array)
sorted(array)