Throw exception on invalid bucket type (#2642)

Signed-off-by: Emmanuel Ferdman <[email protected]>

Author: emmanuel-ferdman

kafka/metrics/stats/percentiles.py

@@ -30,7 +30,7 @@ def __init__(self, size_in_bytes, bucketing, max_val, min_val=0.0,
                                  ' to be 0.0.')
             self.bin_scheme = Histogram.LinearBinScheme(self._buckets, max_val)
         else:
-            ValueError('Unknown bucket type: %s' % (bucketing,))
+            raise ValueError('Unknown bucket type: %s' % (bucketing,))
 
     def stats(self):
         measurables = []