FileDownload does not work with fast-design about panel

[Hoxbro]

Button also break it: pn.widgets.Button(name="Button").servable()

ValueError: ClassSelector parameter 'ReactiveHTMLMetaclass.object' value must be an instance of Viewable, not False.

Traceback (most recent call last):
  File "/home/shh/miniconda3/envs/holoviz/lib/python3.12/site-packages/bokeh/application/handlers/code_runner.py", line 229, in run
    exec(self._code, module.__dict__)
  File "/home/shh/Development/holoviz/example_download_widgets.py", line 16, in <module>
    pn.widgets.Button(name="Button").servable()
  File "/home/shh/projects/holoviz/repos/panel/panel/viewable.py", line 399, in servable
    self.server_doc(title=title, location=location) # type: ignore
    ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/home/shh/projects/holoviz/repos/panel/panel/viewable.py", line 1038, in server_doc
    wrapper = self._design._wrapper(self)
              ^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/home/shh/projects/holoviz/repos/panel/panel/theme/fast.py", line 261, in _wrapper
    return FastWrapper(design=None, object=model, style=self.theme.style)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/home/shh/projects/holoviz/repos/panel/panel/reactive.py", line 1610, in __init__
    super().__init__(**params)
  File "/home/shh/projects/holoviz/repos/panel/panel/reactive.py", line 555, in __init__
    super().__init__(**params)
  File "/home/shh/projects/holoviz/repos/panel/panel/reactive.py", line 117, in __init__
    super().__init__(**params)
  File "/home/shh/projects/holoviz/repos/panel/panel/viewable.py", line 704, in __init__
    super().__init__(**params)
  File "/home/shh/projects/holoviz/repos/panel/panel/viewable.py", line 543, in __init__
    super().__init__(**params)
  File "/home/shh/projects/holoviz/repos/panel/panel/viewable.py", line 304, in __init__
    super().__init__(**params)
  File "/home/shh/projects/holoviz/repos/param/param/parameterized.py", line 4177, in __init__
    refs, deps = self.param._setup_params(**params)
                 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/home/shh/projects/holoviz/repos/param/param/parameterized.py", line 1683, in override_initialization
    ret = fn(self_, *args, **kw)
          ^^^^^^^^^^^^^^^^^^^^^^
  File "/home/shh/projects/holoviz/repos/param/param/parameterized.py", line 1972, in _setup_params
    setattr(self, name, resolved)
  File "/home/shh/projects/holoviz/repos/param/param/parameterized.py", line 528, in _f
    return f(self, obj, val)
           ^^^^^^^^^^^^^^^^^
  File "/home/shh/projects/holoviz/repos/param/param/parameterized.py", line 1495, in __set__
    self._validate(val)
  File "/home/shh/projects/holoviz/repos/param/param/parameters.py", line 2182, in _validate
    self._validate_class_(val, self.class_, self.is_instance)
  File "/home/shh/projects/holoviz/repos/param/param/parameters.py", line 2193, in _validate_class_
    raise ValueError(
ValueError: ClassSelector parameter 'ReactiveHTMLMetaclass.object' value must be an instance of Viewable, not False.

[Hoxbro]

Did you also test the second case?

[philippjfr]

No, but it works.