docs: protected boolean validateAtLeastOneExecutable(BpmnModel bpmnModel, List<ValidationError> errors) {
  	  int nrOfExecutableDefinitions = 0;
  		for (Process process : bpmnModel.getProcesses()) {
  			if (process.isExecutable()) {
  				nrOfExecutableDefinitions++;
  			}
  		}
  		
  		if (nrOfExecutableDefinitions == 0) {
  			addError(errors, Problems.ALL_PROCESS_DEFINITIONS_NOT_EXECUTABLE,
  					"All process definition are set to be non-executable (property 'isExecutable' on process). This is not allowed.");
  		}
  		
  		return nrOfExecutableDefinitions > 0;
    }