[Bug]: Unknown properties return None

Description

Accessing a non-existent property on an API returns None instead of raising an AttributeError

Steps to reproduce

Attempt to access any non-existent attribute on any subclass of AdyenBase

>>> from Adyen import Adyen
>>> api = Adyen(xapikey='token', platform='test')
>>> print(api.foobar)
None
>>> print(api.payment.payments_api.foobar)
None
>>> api.payment.payments_api.fizz()
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
TypeError: 'NoneType' object is not callable

Actual behavior

Attempting to access non-existent attribute returns None. Attempting to call a non-existent method throws a "NoneType object is not callable" error.

Expected behavior

Should return an AttributeError.

Code snippet or screenshots (if applicable)

Root cause is here:

https://github.com/Adyen/adyen-python-api-library/blob/fa8079ff69022117f4375a806ee51e82babce56f/Adyen/services/base.py#L13-L16

If key doesn't exist in self.client, the method exits with no return statement, which is the same as returning None. This means any attribute that's requested defaults to None. It should instead raise AttributeError

Adyen Python API Library version

14.0.0

Python Language version

Python 3.10

Operating System

macOS

Additional context

No response

Start in Adyen/services/base.py at lines 13-16, the root-cause location identified in the issue. Reproduce the missing-attribute examples on AdyenBase subclasses and inspect how unknown keys are handled. Done means nonexistent attributes raise AttributeError instead of returning None, including nested API objects.