Generated Listener code not working for powerbuilder grammar

[raam narayana]

Hi,
I am trying to do translation from powerbuilder(legacy programming language) to java . I am facing issue while tree walking as the listeners are not working

Please find the details for the same

PowerBuilder Grammar I took from antlr4 github repository

https://github.com/antlr/grammars-v4/tree/master/powerbuilder

Source Code
https://github.com/ramnar/antlr/tree/master/powerbuilder/target/generated-sources/antlr4

sample.pba file content

FORWARD INT TEST = 23 END FORWARD

Issue
TreeWalker is invoking only enterStart_rule and enterHeader_rule methods.It is not invoking any other listener methods.In my case enterForward_decl method should be triggered which is not happening. Any pointers way forward are welcome