Kubeflow dsl.IfPresentPlaceholder not working properly in Vertex AI pipelines

Hi,

I am using Kubeflow in Vertex AI pipelines. I tried to use the `dsl.IfPresentPlaceholder` to parameterize some input arguments of the @container_component. It looks like the placeholder is not replaced by the actual value at the runtime, which causes the step execution to fail. I would like to know why this behavior is happening. Does Vertex AI support this feature or this is just Kubeflow native?

#### Environment details

- Python version: `3.9`
- `google-cloud-aiplatform` version: `1.59.0`

#### Code example

I am implementing the placeholder in the following way (dummy example):

```python
@dsl.container_component
def hello_someone(optional_name: str = None):
return dsl.ContainerSpec(
image='python:3.9',
command=[
'say_hello',
dsl.IfPresentPlaceholder(
input_name='optional_name', then=['--name', optional_name])
])
```

I design the pipeline, compile, and run it using the `pipeline_jobs.PipelineJob` method.
When I inspect the logs in Vertex Ai I see that the placeholder is not replaced and it is displayed as:

```
{"IfPresent": {"InputName": "optional_name", "Then": ["--name", "null"]}}
```
In this case I don't pass the `optinal_name` argument on the step.

Thanks,
Joāo