Function groupExist

groupExist(groupId): boolean
JMap.Query.groupExist

Returns true if group exists, else false, for the given group id.
Parameters
- groupId: JId
  The JMap query group id
Returns boolean
Throws
if group id is not correct (invalid format or no resource exists)

Example
```
// returns true if group exists
JMap.Query.groupExist(21)
```