Series.view() without specified dtype
xref https://github.com/pandas-dev/pandas/pull/20220/files#r173655704

Currently, `Series.view()` is actually equivalent to `Series.view('float64')` (because that is the default dtype in the Series constructor) which often does not make sense. Not too important (as there are not many reasons to use this function in pandas), but I think we should fix to either a) disallow `dtype=None` or either b) if dtype is None to set `dtype = self.dtype` (behaviour of numpy if no dtype is specified)