`TypeError: unsupported operand type(s) for +=: 'NoneType' and 'str'` during client initialization (v0.16.2)

[disenchant]

Description:
Since the release of version 0.16.2 (and currently on master), importing the V2 Client crashes with a TypeError.

This occurs because the OpenAPI specification shipped with the package (openapi.json) now contains request body properties that define an enum but do not provide a description.

When the dynamic API client generator parses these properties, it attempts to append the enum choices to a None description, causing the crash during the module import phase.

Steps to Reproduce:
Simply importing the client in an environment with exoscale==0.16.2 triggers the error:

from exoscale.api.v2 import Client

Stack Trace:

Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/usr/local/lib/python3.14/site-packages/exoscale/api/v2.py", line 97, in <module>
    BaseClient = create_client_class(api_spec)
  File "/usr/local/lib/python3.14/site-packages/exoscale/api/generator.py", line 354, in create_client_class
    op_fn = _create_operation_call(
        py_operation_name,
        operation_name,
        operation,
        api_spec,
    )
  File "/usr/local/lib/python3.14/site-packages/exoscale/api/generator.py", line 243, in _create_operation_call
    desc += f". Must be one of ``{choices}``"
TypeError: unsupported operand type(s) for +=: 'NoneType' and 'str'

Root Cause & Location:
The bug is located in exoscale/api/generator.py inside the _create_operation_call function (around line 242):

        for name, prop in properties.items():
            # ...
            desc = prop.get("description") # <-- Returns None if missing
            if "enum" in item:
                choices = "``, ``".join(map(repr, item["enum"]))
                desc += f". Must be one of ``{choices}``" # <-- Crashes: None += str

Proposed Fix:
Ensure desc is initialized as an empty string if it is missing from the spec.

In exoscale/api/generator.py:

-           desc = prop.get("description")
+           desc = prop.get("description") or ""
            if "enum" in item: