hbase ERROR: wrong number of arguments (3 for 4)

hbase(main):036:0> get 'ddl', 'example', 'info:age'
COLUMN                                               CELL
info:age                                            timestamp=1436787562408, value=\x00\x00\x00\x00\x00\x00\x00\x03
1 row(s) in 0.0160 seconds

hbase(main):037:0> get_counter 'ddl', 'example', 'info:age'

ERROR: wrong number of arguments (3 for 4)

Here is some help for this command:
Return a counter cell value at specified table/row/column coordinates.
A cell cell should be managed with atomic increment function oh HBase
and the data should be binary encoded. Example:

hbase> get_counter 'ns1:t1', 'r1', 'c1'
  hbase> get_counter 't1', 'r1', 'c1'

The same commands also can be run on a table reference. Suppose you had a reference
t to table 't1', the corresponding command would be:

hbase> t.get_counter 'r1', 'c1'

hbase(main):041:0> get_counter 'ddl', 'example', 'info:age', 'dummy'   <----加上dummy就对了
COUNTER VALUE = 3

hbase(main):042:0> get 'ddl', 'example', 'info:age'
COLUMN                                               CELL
info:age                                            timestamp=1436787562408, value=\x00\x00\x00\x00\x00\x00\x00\x03
1 row(s) in 0.0210 seconds

hbase(main):043:0> truncate 'ddl'
Truncating 'ddl' table (it may take a while):
- Disabling table...
- Dropping table...
- Creating table...
0 row(s) in 2.6630 seconds

hbase(main):044:0>