public Set<String> usersWithGrant(Grant grant){
        if (grant==null) throw new IllegalArgumentException("grant cannot be null");
        return userGrants.get(grant);
    }
public Set < String > usersWithGrant ( Grant grant ) { if ( grant == null ) throw new IllegalArgumentException ( "grant cannot be null" ) ; return userGrants . get ( grant ) ; }
Returns the users that have the specified {@code grant}
@param grant a {@link com.baasbox.android.Grant}
@return