Shared pool Free percentage greater than 100

 Hello ,
The value of "Shared Pool Free %" in v$sysmetric is larger than 100%
SQL> select value, group_id from v$sysmetric where metric_name = 'Shared Pool Free %';
VALUE GROUP_ID
186.45107 2
186.4685382 3

SQL> show parameter shared_pool

NAME TYPE VALUE
-------------- ------------ --
shared_pool_reserved_size big integer 832149913
shared_pool_size big integer 0

SQL> show sga

Total System Global Area 1.0155E+11 bytes
Fixed Size 2163880 bytes
Variable Size 8.1068E+10 bytes
Database Buffers 2.0401E+10 bytes
Redo Buffers 79310848 bytes

Any clue?

Thanks,