function getNextReleaseTimeOf (address account, address tokenAddr)
        external
        view
        returns (uint256) 
    {
        require(account != address(0x0));

        uint256 nextRelease = 2**256 - 1;
        for (uint256 i = 0; i < lockedBalances[account][tokenAddr].length; i++) {
            if (lockedBalances[account][tokenAddr][i].releaseTime > block.timestamp &&
               lockedBalances[account][tokenAddr][i].releaseTime < nextRelease) {

                nextRelease = lockedBalances[account][tokenAddr][i].releaseTime;
            }
        }

        
        if (nextRelease == 2**256 - 1) {
            nextRelease = 0;
        }
        return nextRelease;
    }