Jenkinsfile + Slack: avisa solo cuando cambio el estado del build

Jenkinsfile

#!groovy

stage 'build and tests'

def project
def slack

node {
    def workspace = pwd()
    slack   = load "${workspace}@script/slack.groovy"
    project = load "${workspace}@script/project.groovy"

    try {
        //get things done
    } catch (e) {
        currentBuild.result = "FAILED"
        throw e
    } finally {
        slack.notifyToSlack(currentBuild.result)
    }
}

slack.groovy

def getLastBuildStatus() {
    return currentBuild.rawBuild.getPreviousBuild()?.getResult().toString()
}

def notifyToSlack(String buildStatus = 'STARTED') {
    buildStatus =  buildStatus ?: 'SUCCESS'
    if (mustNotify(buildStatus)) {
        def color = getColorByStatus(buildStatus)
        slackSend(message: "${env.JOB_NAME} - #${env.BUILD_NUMBER} - ${buildStatus}",
                channel: "#your-channel", color: color, token: "yourToken")
        return
    }
    echo "No debe notificar por Slack"
}

def getColorByStatus(String buildStatus = 'STARTED') {
    if (buildStatus == 'STARTED') {
        //amarillo
        colorCode = '#FFFF00'
    } else if (buildStatus == 'SUCCESS') {
        //verde
        colorCode = '#00FF00'
    } else {
        //rojo
        colorCode = '#FF0000'
    }
    return colorCode;
}

def mustNotify(String buildStatus) {
    def lastBuildStatus = getLastBuildStatus()
    return !buildStatus.equals(lastBuildStatus)
}

return this