function emitMsg(msg, node) {
    if ( node._ui === undefined && node.passthrough === true) return

    // Merge input msg and ._ui to create new output msg
    const msg2 = {
        ...msg,
        ...{
            _ui: node._ui,
        }
    }

    // Remove payload unless requested
    if (node.passthrough !== true) delete msg2.payload

    // Add default topic if defined and if not overridden by input msg
    // NB: Needs to be unique if using uib-cache
    if (!msg2.topic && node.topic !== '') msg2.topic = node.topic

    node.send(msg2)
}
Build the output and send the msg (clone input msg and add _ui prop)
@param {*} msg The input or custom event msg data
@param {runtimeNode & uibElNode} node reference to node instance