After upgrade, Bamboo Java Spec failed, no ScriptBuildTask generated

[Tech Noboundary]

Alright, this is resolved.  There are further error messages in the Bamboo server log.  Not sure why they were not pulled to the build log. 

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Bamboo upgraded from 6.8.2 to 7.2.1

We have been useing Bamboo Java Spec.  After upgrade, the build will fail with the following log messages.

simple	03-Mar-2021 13:55:46	User xxxx is moving build BB-BBB-JOB1-27
simple	03-Mar-2021 14:21:46	Build Branch Builds - Branch Build BJS - Default Job #27 (BB-BBB-JOB1-27) started building on agent Remote for Build Branch 53, bamboo version: 7.2.1
simple	03-Mar-2021 14:21:46	
simple	03-Mar-2021 14:21:46	Build working directory is D:\Bamboo\build-dir\BB-BBB-JOB1
simple	03-Mar-2021 14:21:47	Executing build Branch Builds - Branch Build BJS - Default Job #27 (BB-BBB-JOB1-27)
simple	03-Mar-2021 14:21:47	Running pre-build action: VCS Version Collector
simple	03-Mar-2021 14:21:47	Running pre-build action: Artifactory Release Staging
simple	03-Mar-2021 14:21:47	Starting task 'Listener' of type 'com.atlassian.bamboo.plugins.scripttask:task.builder.script'
command	03-Mar-2021 14:21:47	Beginning to execute external process for build 'Branch Builds - Branch Build BJS - Default Job #27 (BB-BBB-JOB1-27)'\n ... running command line: \nD:\Atlassian\bamboo-home\temp\BB-BBB-JOB1-27-ScriptBuildTask-2715883387375057947.ps1\n ... in: D:\Bamboo\build-dir\BB-BBB-JOB1\n
build	03-Mar-2021 14:21:54	 :0 :  ::  :0 :
build	03-Mar-2021 14:21:54	Both revision can not be blank!! Branch has been deleted for sure.  Exiting out.
simple	03-Mar-2021 14:21:54	Failing task since return code of [powershell -NonInteractive -ExecutionPolicy bypass -Command D:\Atlassian\bamboo-home\temp\BB-BBB-JOB1-27-ScriptBuildTask-2715883387375057947.ps1] was 1 while expected 0
simple	03-Mar-2021 14:21:54	Finished task 'Listener' with result: Failed

Looking into bamboo-home\temp, there is no BB-BBB-JOB1-27-ScriptBuildTask-2715883387375057947.ps1 file. 

What could be the reason of failure?  And what are necessary steps to debug this? 

Meanwhile, I found once that there was a bamboo.specs.enabled variable showing in the audio log.  It was first "false" and then can be toggled to be "null" through GUI.  However, the option only showed up once in one branch creation and there is no trace of how it works. 

Regards,

[Tech Noboundary]

Additional info. 

Furthermore, Bamboo\build-dir\BB-BBB-JOB1 is empty. 

mvn test and mvn -Ppublish-specs are all successful w/o any error.