我正在通过jenkins调用Powershell脚本，并且从powershell脚本获取输出值，似乎发生的是，如果由于某种原因输出值为null，则jenkins管道将失败，并出现以下错误。

代码可以在下面找到

     stage('Get Ticket Number') {
         steps {
             script {
                env.New_Ticket = powershell(returnStdout: true,script: '.\\New_Ticket.ps1')
             }
         }
     }

def ticket_json = readJSON文本：“ $ {env.New_Ticket}” 回声“ Ticket：” + ticket_json.ticketno

错误详细信息可以在下面找到。

hudson.remoting.ProxyException: net.sf.json.JSONException: Invalid JSON String
    at net.sf.json.JSONSerializer.toJSON(JSONSerializer.java:143)
    at net.sf.json.JSONSerializer.toJSON(JSONSerializer.java:103)
    at net.sf.json.JSONSerializer.toJSON(JSONSerializer.java:84)
    at org.jenkinsci.plugins.pipeline.utility.steps.json.ReadJSONStepExecution.doRun(ReadJSONStepExecution.java:79)
    at org.jenkinsci.plugins.pipeline.utility.steps.json.ReadJSONStepExecution.doRun(ReadJSONStepExecution.java:48)
    at org.jenkinsci.plugins.pipeline.utility.steps.AbstractFileOrTextStepExecution.run(AbstractFileOrTextStepExecution.java:32)
    at org.jenkinsci.plugins.workflow.steps.SynchronousnonBlockingStepExecution.lambda$start$0(SynchronousnonBlockingStepExecution.java:47)
    at java.util.concurrent.Executors$RunnableAdapter.call(Executors.java:511)
    at java.util.concurrent.Futuretask.run(Futuretask.java:266)
    at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1149)
    at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:624)
    at java.lang.Thread.run(Thread.java:748)
Finished: FAILURE