`fix-mutable-params` results in `AttributeError`

[drdavella]

Description

The fix-mutable-params codemod appears to result in an AttributeError in certain circumstances. This was originally detected while processing this open source project: https://github.com/zulip/zulip

After checking out use the following command to reproduce:

codemodder /PATH/TO/zulip --codemod-include=fix-mutable-params

It will be necessary to come up with a unit test that minimally reproduces the problem and then fix it.

Traceback

 File "/Users/danieldavella/miniconda3/envs/test-python-codemod-package/lib/python3.10/site-packages/libcst/matchers/_visitors.py", line 515, in on_leave
    retval = CSTTransformer.on_leave(self, original_node, updated_node)
  File "/Users/danieldavella/miniconda3/envs/test-python-codemod-package/lib/python3.10/site-packages/libcst/_visitors.py", line 71, in on_leave
    updated_node = leave_func(original_node, updated_node)
  File "/Users/danieldavella/codemodder-python/src/core_codemods/fix_mutable_params.py", line 180, in leave_FunctionDef
    body=updated_node.body.with_changes(body=new_body),
  File "/Users/danieldavella/miniconda3/envs/test-python-codemod-package/lib/python3.10/site-packages/libcst/_nodes/base.py", line 325, in with_changes
    return replace(self, **changes)
  File "/Users/danieldavella/miniconda3/envs/test-python-codemod-package/lib/python3.10/dataclasses.py", line 1453, in replace
    return obj.__class__(**changes)
  File "<string>", line 6, in __init__
  File "/Users/danieldavella/miniconda3/envs/test-python-codemod-package/lib/python3.10/site-packages/libcst/_nodes/base.py", line 117, in __post_init__
    self._validate()
  File "/Users/danieldavella/miniconda3/envs/test-python-codemod-package/lib/python3.10/site-packages/libcst/_nodes/statement.py", line 390, in _validate
    if small_stmt.semicolon is None:
AttributeError: 'SimpleStatementLine' object has no attribute 'semicolon'