code: private ProcessExtensionModel convertJsonVariables(ProcessExtensionModel processExtensionModel){
          if( processExtensionModel!=null && processExtensionModel.getExtensions()!=null
                  && processExtensionModel.getExtensions().getProperties()!=null ){
  
              for(VariableDefinition variableDefinition:processExtensionModel.getExtensions().getProperties().values()){
                  if(!variableTypeMap.keySet().contains(variableDefinition.getType())||variableDefinition.getType().equals("json")){
                      variableDefinition.setValue(objectMapper.convertValue(variableDefinition.getValue(), JsonNode.class));
                  }
              }
          }
          return processExtensionModel;
      }
docs: Json variables need to be represented as JsonNode for engine to handle as Json
  Do this for any var marked as json or whose type is not recognised from the extension file