Consider a different version output if no properties are set

[ullenboom]

By default, the version command is active. However, without any properties set, the output might
surprise:

version
2022-02-04 19:48:59.496 ERROR 179596 --- [           main] .TemplateExecutor$LoggingSTErrorListener : runTimeError [context [anonymous] 1:4 attribute buildVersion isn't defined]
2022-02-04 19:48:59.497 ERROR 179596 --- [           main] .TemplateExecutor$LoggingSTErrorListener : runTimeError [context [anonymous] 4:4 attribute buildGroup isn't defined]
2022-02-04 19:48:59.497 ERROR 179596 --- [           main] .TemplateExecutor$LoggingSTErrorListener : runTimeError [context [anonymous] 7:4 attribute buildArtifact isn't defined]
2022-02-04 19:48:59.497 ERROR 179596 --- [           main] .TemplateExecutor$LoggingSTErrorListener : runTimeError [context [anonymous] 10:4 attribute buildName isn't defined]
2022-02-04 19:48:59.497 ERROR 179596 --- [           main] .TemplateExecutor$LoggingSTErrorListener : runTimeError [context [anonymous] 13:4 attribute buildTime isn't defined]
2022-02-04 19:48:59.497 ERROR 179596 --- [           main] .TemplateExecutor$LoggingSTErrorListener : runTimeError [context [anonymous] 16:4 attribute gitShortCommitId isn't defined]
2022-02-04 19:48:59.497 ERROR 179596 --- [           main] .TemplateExecutor$LoggingSTErrorListener : runTimeError [context [anonymous] 19:4 attribute gitCommitId isn't defined]
2022-02-04 19:48:59.497 ERROR 179596 --- [           main] .TemplateExecutor$LoggingSTErrorListener : runTimeError [context [anonymous] 22:4 attribute gitBranch isn't defined]
2022-02-04 19:48:59.497 ERROR 179596 --- [           main] .TemplateExecutor$LoggingSTErrorListener : runTimeError [context [anonymous] 25:4 attribute gitCommitTime isn't 

I am not sure if ERROR is the appropriate log level. Maybe change to WARNING or find a more compact way to express that no data exists for a version string. Or maybe don't activate the version command if the properties are not set.

[jvalkeal]

You're right that it's not an error as we know stringtemplate from antlr will report those as errors. We added that listener as otherwise antlr printed those into stderr. We could set attributes to nulls and also tweak logging levels.