code: Bucket getBucketForKey(Object key)
      {
          int index = getBucketIndexForKey(key);
  
          Bucket bucket = buckets[index];
          if (bucket == null)
          {
              synchronized (bucketLock)
              {
                  bucket = buckets[index];
              }
          }
  
          return bucket;
      }
docs: Returns the bucket which the specified key hashes to. <p>
  
  @param key key for the object to get a bucket for.
  
  @return the bucket which the specified key hashes to.