Different behavior on merge function between the JS lib and the Python lib

Hi

**Environment:** Python 3.11.9 + pip 24.3.1
**LIbrary:** jmespath 1.0.1

I'm trying to use jmespath to extract some fields from the JSON file. But I got differnt results from the JS library and Python library.
[test.json](https://github.com/user-attachments/files/17879126/test.json)

```jmespath
merge(
{
type: type,
id: id_str
},
modules.module_dynamic.{
title: major.opus.title || archive.title || `发布了动态`,
desc: major.opus.summary.text || major.archive.desc,
covers: major.opus.pics[].url[] || major.archive.covers[]
},
orig.modules.module_dynamic.{
title: major.opus.title || archive.title || `转发了动态`,
desc: major.opus.summary.text || major.archive.desc,
covers: major.opus.pics[].url[] || major.archive.covers[]
},
modules.module_author.{
time: pub_ts
},
modules.module_stat.{
stat: {
like: like.count,
comment: comment.count,
forward: forward.count
}
}
)
```

It's ok, when I use jmespath playground.

But when I use the python lib, I got this type error. Looks likes the python library don't merge none values in the merge function.

```log
.venv/lib/python3.11/site-packages/jmespath/__init__.py:12: in search
return parser.Parser().parse(expression).search(data, options=options)
.venv/lib/python3.11/site-packages/jmespath/parser.py:509: in search
result = interpreter.visit(self.parsed, value)
.venv/lib/python3.11/site-packages/jmespath/visitor.py:94: in visit
return method(node, *args, **kwargs)
.venv/lib/python3.11/site-packages/jmespath/visitor.py:171: in visit_function_expression
return self._functions.call_function(node['value'], resolved_args)
.venv/lib/python3.11/site-packages/jmespath/functions.py:81: in call_function
return function(self, *resolved_args)
_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _

self =
arguments = ({'id': '1000725331289571330', 'type': 'DYNAMIC_TYPE_DRAW'}, {'covers': ['http://i0.hdslb.com/bfs/new_dyn/10686e544526...greatest evil.', 'title': '发布了动态'}, None, {'time': 1731837923}, {'stat': {'comment': 276, 'forward': 5, 'like': 1784}})
merged = {'covers': ['http://i0.hdslb.com/bfs/new_dyn/10686e544526539b0da871b41339d83a389245745.png'], 'desc': '第六集又双叒叕看爽了[脱单do...s us to our greatest good is also the cause of our greatest evil.', 'id': '1000725331289571330', 'title': '发 布了动态', ...}
arg = None

@signature({"types": ["object"], "variadic": True})
def _func_merge(self, *arguments):
merged = {}
for arg in arguments:
> merged.update(arg)
E TypeError: 'NoneType' object is not iterable

.venv/lib/python3.11/site-packages/jmespath/functions.py:266: TypeError
```