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Review the following code diff in the file "g4f/Provider/Mhystical.py" and take the pull request title and description into account when writing the response.
  
Pull request title: [pull] main from xtekky:main
Pull request description:
---
See Commits and Changes for more details.

-----
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---

Each line is prefixed by its number. Code to review:
```
1:+from __future__ import annotations
2:+
3:+import json
4:+import logging
5:+from aiohttp import ClientSession
6:+from ..typing import AsyncResult, Messages
7:+from .base_provider import AsyncGeneratorProvider, ProviderModelMixin
8:+from .helper import format_prompt
9:+
10:+"""
11:+    Mhystical.cc
12:+    ~~~~~~~~~~~~
13:+    Author: NoelP.dev
14:+    Last Updated: 2024-05-11
15:+    
16:+    Author Site: https://noelp.dev
17:+    Provider Site: https://mhystical.cc
18:+
19:+"""
20:+
21:+logger = logging.getLogger(__name__)
22:+
23:+class Mhystical(AsyncGeneratorProvider, ProviderModelMixin):
24:+    url = "https://api.mhystical.cc"
25:+    api_endpoint = "https://api.mhystical.cc/v1/completions"
26:+    working = True
27:+    supports_stream = False  # Set to False, as streaming is not specified in ChatifyAI
28:+    supports_system_message = False
29:+    supports_message_history = True
30:+    
31:+    default_model = 'gpt-4'
32:+    models = [default_model]
33:+    model_aliases = {}
34:+
35:+    @classmethod
36:+    def get_model(cls, model: str) -> str:
37:+        if model in cls.models:
38:+            return model
39:+        elif model in cls.model_aliases:
40:+            return cls.model_aliases.get(model, cls.default_model)
41:+        else:
42:+            return cls.default_model
43:+
44:+    @classmethod
45:+    async def create_async_generator(
46:+        cls,
47:+        model: str,
48:+        messages: Messages,
49:+        proxy: str = None,
50:+        **kwargs
51:+    ) -> AsyncResult:
52:+        model = cls.get_model(model)
53:+        
54:+        headers = {
55:+            "x-api-key": "mhystical",
56:+            "Content-Type": "application/json",
57:+            "accept": "*/*",
58:+            "cache-control": "no-cache",
59:+            "origin": cls.url,
60:+            "referer": f"{cls.url}/",
61:+            "user-agent": "Mozilla/5.0 (X11; Linux x86_64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/129.0.0.0 Safari/537.36"
62:+        }
63:+        
64:+        async with ClientSession(headers=headers) as session:
65:+            data = {
66:+                "model": model,
67:+                "messages": [{"role": "user", "content": format_prompt(messages)}]
68:+            }
69:+            async with session.post(cls.api_endpoint, json=data, headers=headers, proxy=proxy) as response:
70:+                if response.status == 400:
71:+                    yield "Error: API key is missing"
72:+                elif response.status == 429:
73:+                    yield "Error: Rate limit exceeded"
74:+                elif response.status == 500:
75:+                    yield "Error: Internal server error"
76:+                else:
77:+                    response.raise_for_status()
78:+                    response_text = await response.text()
79:+                    filtered_response = cls.filter_response(response_text)
80:+                    yield filtered_response
81:+
82:+    @staticmethod
83:+    def filter_response(response_text: str) -> str:
84:+        try:
85:+            json_response = json.loads(response_text)
86:+            message_content = json_response["choices"][0]["message"]["content"]
87:+            return message_content
88:+        except (KeyError, IndexError, json.JSONDecodeError) as e:
89:+            logger.error("Error parsing response: %s", e)
90:+            return "Error: Failed to parse response from API."
```