Use dt units in empty() (tz path) (#893)

* Use dt units in empty()

* simplfiying suggestion

* fix

fastparquet/dataframe.py

@@ -5,7 +5,8 @@
 from pandas import (
     Categorical, DataFrame, Series,
     CategoricalIndex, RangeIndex, Index, MultiIndex,
-    DatetimeIndex, CategoricalDtype
+    DatetimeIndex, CategoricalDtype,
+    DatetimeTZDtype
 )
 from pandas.core.arrays.masked import BaseMaskedDtype
 import warnings
@@ -195,9 +196,10 @@ def set_cats(values, i=i, col=col, **kwargs):
 
             values = Categorical.from_codes(codes=code, dtype=bvalues.dtype)
 
-        elif getattr(bvalues.dtype, 'tz', None):
-            values = np.zeros(shape=shape, dtype='M8[ns]')
-            values = type(bvalues)(values, dtype=bvalues.dtype)
+        elif isinstance(bvalues.dtype, DatetimeTZDtype):
+            dt = "M8[ns]" if PANDAS_VERSION.major < 2 else f'M8[{bvalues.dtype.unit}]'
+            values = np.zeros(shape=shape, dtype=dt)
+            values = type(bvalues)._from_sequence(values, copy=False, dtype=bvalues.dtype)
         else:
             if not isinstance(bvalues, np.ndarray):
                 # e.g. DatetimeLikeBlock backed by DatetimeArray/TimedeltaArray