def tz_to_dtype(tz):
if tz is None:<EOL><INDENT>return _NS_DTYPE<EOL><DEDENT>else:<EOL><INDENT>return DatetimeTZDtype(tz=tz)<EOL><DEDENT>
Return a datetime64[ns] dtype appropriate for the given timezone.

Parameters
----------
tz : tzinfo or None

Returns
-------
np.dtype or Datetime64TZDType