Revert "return 0 for instead of None"

This reverts commit 4afceab.

Author: GitHub Revert Action

RucioClient.py

@@ -91,10 +91,8 @@ def getFileCountPerBlock(self, dataset):
             blocks = []
             for block in self.getBlockNamesDataset(dataset):
                 blocks.append((block, self.getFileCountBlock(block)))
-            if blocks is None:
-                raise Exception("number of file count per block is None")
         except Exception as e:
             print(str(e))
-            return 0
+            return []
         return blocks