JMESPath parse issue when using join function

Hi, I'm getting the following error when reading logs from AppRunner:

Affected log line:

```
{'@timestamp': '2024-09-05T15:09:20.073Z', '@version': '1', 'logger_name': 'com.xxx.controller.authentication.JwtController', 'thread_name': 'http-nio-8080-exec-176', 'level': 'ERROR', 'level_value': 40000, 'application': 'xxxx'}
```

Query:

```
join(``, [(level == `WARN` && `\\u001b[33m` || level == `ERROR` && `\\u001b[31m` || level == `DEBUG` && `\\u001b[36m` || level == `INFO` && `\\u001b[32m` || ``), `[`, level, `] `, `\\u001b[0m`, `[`, thread_name, `] `, logger_name, `\\n`, message])
```

```
You've found a bug! Please, raise an issue attaching the following traceback
https://github.com/jorgebastida/awslogs/issues/new

Version: 0.15.0
Python: 3.12.5 (main, Aug 9 2024, 08:20:41) [GCC 14.2.1 20240805]
boto3 version: 1.35.12
Platform: Linux-5.15.153.1-microsoft-standard-WSL2-x86_64-with-glibc2.39 (I wish it was real linux)
Args: ['/home/davide.depau/test/venv/bin/awslogs', 'get', '-s', '1h', '-w', '-G', '--timestamp', '-q', 'join(``, [(level == `WARN` && `\\u001b[33m` || level == `ERROR` && `\\u001b[31m` || level == `DEBUG` && `\\u001b[36m` || level == `INFO` && `\\u001b[32m` || ``), `[`, level, `] `, `\\u001b[0m`, `[`, thread_name, `] `, logger_name, `\\n`, message])', '/aws/apprunner/REDACTED/REDACTED/application']
Config: {options}

Traceback (most recent call last):
File "/home/davide.depau/test/venv/lib/python3.12/site-packages/awslogs/bin.py", line 210, in main
getattr(logs, options.func)()
File "/home/davide.depau/test/venv/lib/python3.12/site-packages/awslogs/core.py", line 219, in list_logs
consumer()
File "/home/davide.depau/test/venv/lib/python3.12/site-packages/awslogs/core.py", line 202, in consumer
message = self.query_expression.search(parsed)
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
File "/home/davide.depau/test/venv/lib/python3.12/site-packages/jmespath/parser.py", line 509, in search
result = interpreter.visit(self.parsed, value)
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
File "/home/davide.depau/test/venv/lib/python3.12/site-packages/jmespath/visitor.py", line 94, in visit
return method(node, *args, **kwargs)
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
File "/home/davide.depau/test/venv/lib/python3.12/site-packages/jmespath/visitor.py", line 171, in visit_function_expression
return self._functions.call_function(node['value'], resolved_args)
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
File "/home/davide.depau/test/venv/lib/python3.12/site-packages/jmespath/functions.py", line 80, in call_function
self._validate_arguments(resolved_args, signature, function_name)
File "/home/davide.depau/test/venv/lib/python3.12/site-packages/jmespath/functions.py", line 91, in _validate_arguments
return self._type_check(args, signature, function_name)
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
File "/home/davide.depau/test/venv/lib/python3.12/site-packages/jmespath/functions.py", line 97, in _type_check
self._type_check_single(actual[i], allowed_types,
File "/home/davide.depau/test/venv/lib/python3.12/site-packages/jmespath/functions.py", line 120, in _type_check_single
self._subtype_check(current, allowed_subtypes,
File "/home/davide.depau/test/venv/lib/python3.12/site-packages/jmespath/functions.py", line 144, in _subtype_check
raise exceptions.JMESPathTypeError(
jmespath.exceptions.JMESPathTypeError: In function join(), invalid type for value: None, expected one of: ['array-string'], received: "NoneType"
```

I have `jmespath==1.0.1`.