code: function (connectionName, cb) {
              var closeConnection = function (connectionName) {
                  var connection = me.connections[connectionName];
                  if (connection) {
                      if (connection.conn && typeof connection.conn.close === 'function') {
                          connection.conn.close(function (err) {
                              if (err) console.error(err);
                          });
                      }
                      else {
                          connection.close(function (err) {
                              if (err) console.error(err);
                          });
                      }
                  }
  
                  delete me.connections[connectionName];
              };
  
              if (connectionName) closeConnection(connectionName);
              else _.each(me.connections, closeConnection);
  
              return cb();
          }
docs: Fired when a model is unregistered, typically when the server
  is killed. Useful for tearing-down remaining open connections,
  etc.
  
  @param  {Function} cb [description]
  @return {[type]}      [description]