quantity_input fails when no annotations are present on keyword only arguments #7551

>>> @u.quantity_input
    def test(a: u.pix, *, bob):
        print(a, bob)
        
xonsh: To log full traceback to a file set: $XONSH_TRACEBACK_LOGFILE = <filename>
Traceback (most recent call last):
  File "/usr/lib/python3.6/site-packages/xonsh/__amalgam__.py", line 14901, in default
    run_compiled_code(code, self.ctx, None, 'single')
  File "/usr/lib/python3.6/site-packages/xonsh/__amalgam__.py", line 2326, in run_compiled_code
    func(code, glb, loc)
  File "<xonsh-code>", line 2, in <module>
  File "/usr/lib/python3.6/site-packages/astropy/units/decorators.py", line 147, in as_decorator
    return self(func)
  File "/usr/lib/python3.6/site-packages/astropy/units/decorators.py", line 161, in __call__
    @wraps(wrapped_function)
  File "/usr/lib/python3.6/site-packages/astropy/utils/decorators.py", line 819, in wraps
    wrapped_args = _get_function_args(wrapped, exclude_args=exclude_args)
  File "/usr/lib/python3.6/site-packages/astropy/utils/decorators.py", line 866, in _get_function_args
    all_args = _get_function_args_internal(func)
  File "/usr/lib/python3.6/site-packages/astropy/utils/decorators.py", line 859, in _get_function_args_internal
    for argname in argspec.kwonlyargs)
  File "/usr/lib/python3.6/site-packages/astropy/utils/decorators.py", line 859, in <genexpr>
    for argname in argspec.kwonlyargs)
TypeError: 'NoneType' object is not subscriptable