Moved conversion to if percentiles is not None

Author: pbreach

pandas/core/generic.py

@@ -5255,16 +5255,16 @@ def abs(self):
 
     @Appender(_shared_docs['describe'] % _shared_doc_kwargs)
     def describe(self, percentiles=None, include=None, exclude=None):
-        # explicit conversion of `percentiles` to list
-        percentiles = list(percentiles)
-
         if self.ndim >= 3:
             msg = "describe is not implemented on Panel or PanelND objects."
             raise NotImplementedError(msg)
         elif self.ndim == 2 and self.columns.size == 0:
             raise ValueError("Cannot describe a DataFrame without columns")
 
         if percentiles is not None:
+            # explicit conversion of `percentiles` to list
+            percentiles = list(percentiles)
+
             # get them all to be in [0, 1]
             self._check_percentile(percentiles)