BUG-23282 calling min on series of NaT returns NaT

Author: JustinZhengBC

pandas/core/nanops.py

@@ -718,6 +718,8 @@ def reduction(values, axis=None, skipna=True, mask=None):
                 result = np.nan
         else:
             result = getattr(values, meth)(axis)
+            if is_integer(result) and result == _int64_max:
+                result = tslibs.iNaT
 
         result = _wrap_results(result, dtype)
         return _maybe_null_out(result, axis, mask)