code: public void verifyProcessDefinitionsDoNotShareKeys(
        Collection<ProcessDefinitionEntity> processDefinitions) {
      Set<String> keySet = new LinkedHashSet<String>();
      for (ProcessDefinitionEntity processDefinition : processDefinitions) {
        if (keySet.contains(processDefinition.getKey())) {
          throw new ActivitiException(
              "The deployment contains process definitions with the same key (process id attribute), this is not allowed");
        }
        keySet.add(processDefinition.getKey());
      }
    }
docs: Verifies that no two process definitions share the same key, to prevent database unique
  index violation.
  
  @throws ActivitiException if any two processes have the same key