Intellij Custom Language runtime error: Caused by: java.lang.NoClassDefFoundError:

I'm developing a custom language plugin for intellij idea (using the ANTLR adaptor ) it compiles properly but it throws this error when loading:

2020-11-19 11:35:15,675 [ 3952] ERROR - i.util.KeyedExtensionCollector - Could not initialize class net.hexah.sourcepawn.SourcePawnParserDefinition [Plugin: net.hexah.sourcepawn]

And in the sandbox when the caret changes this is thrown:

ERROR - aemon.impl.PassExecutorService - Argument for @NotNull parameter 'future' of com/intellij/openapi/progress/util/ProgressIndicatorUtils.awaitWithCheckCanceled must not be null 

I've shared here the relevant files: https://gist.github.com/Hexer10/5fe21deb9049cfbc08ec5ff79600b2c8

I've tried setting up breakpoints all round the code in the parser class, but none of them got hit.

Note: The Grammar is a modified version of the ANTLR C grammar and the highlighting is still working but the IDE keeps hanging on Analyzing