java.lang.NullPointerException：无法调用方法

Question

有一个下一个字段，我试图将其工作的闲置结果发送出去

        }  finally {
            sh(script: 'ls -lah')
            slack.jobResultNotification(currentBuild.result, '#some_channel',null,null,null,'https://hooks.slack.com/services/XXXXXX/XXXXXX/XXXXXXX')
        }
    }

但是每次我得到

java.lang.NullPointerException: Cannot invoke method getSecret() on null object

松弛通知功能（我只添加了代码的重要部分）

def jobResultNotification(String buildStatusParam, String channel = "#some_channel",
                          String jobName=null,
                          Number buildNumber=null, String buildUrl=null,
                          String credentialsId="SLACK_WEBHOOK_URL") {
    def jobNameParam = jobName != null && jobName != "" ? jobName : env.JOB_NAME
    def buildUrlParam = buildUrl != null && buildUrl != "" ? buildUrl : env.BUILD_URL
    def buildNumberParam = buildNumber != null && buildNumber != "" ? buildNumber : env.BUILD_NUMBER

    def common = new com.Common()
    cred = common.getCredentialsById(credentialsId)
    hook_url_parsed = cred.getSecret().toString()

}   

还有信誉

def getCredentialsById(String credsId, String credsType = 'any') {
    def credClasses = [ // ordered by class name
                        sshKey    : com.cloudbees.jenkins.plugins.sshcredentials.impl.BasicSSHUserPrivateKey.class,
                        cert      : com.cloudbees.plugins.credentials.common.CertificateCredentials.class,
                        password  : com.cloudbees.plugins.credentials.common.StandardUsernamePasswordCredentials.class,
                        any       : com.cloudbees.plugins.credentials.impl.BaseStandardCredentials.class,
                        dockerCert: org.jenkinsci.plugins.docker.commons.credentials.DockerServerCredentials.class,
                        file      : org.jenkinsci.plugins.plaincredentials.FileCredentials.class,
                        string    : org.jenkinsci.plugins.plaincredentials.StringCredentials.class,
    ]
    return com.cloudbees.plugins.credentials.CredentialsProvider.lookupCredentials(
        credClasses[credsType],
        jenkins.model.Jenkins.instance
    ).findAll { cred -> cred.id == credsId }[0]
}