Custom components: Adding warning when not all inputs can be obtained

[CharlesCousyn]

Is your feature request related to a problem? Please describe.
Here a simplified RAG pipeline (where a directly inject documents for testing):

The purpose of the latter is to offer a way of bypassing the generator when no documents is available using a ConditionalRouter.

The very last component of the pipeline is a custom component whose aim is to aggregate all variables in a payload that will be provided to build an API . Its code is as follows:

@component
class PayloadBuilder2:
    """
    A component to build the payload
    """

    @component.output_types(payload=Dict)
    def run(
            self,
            documents: List[Document],
            replies: List[ChatMessage],
            no_documents: str,
    ):
        print("PayloadBuilder.run")
        return {
            "payload": {
                "documents": documents,
                "no_documents": no_documents,
                "replies": replies,
            }
        }

The problem is that no matter what we send, the pipeline will return an empty dictionary:

{}

By debugging, i found that the the reason is that my custom component necessarily expects to have a value for no_documents input in order to be allowed to run.
The fix in my case was the following:
Replace:

   no_documents: str,

By

   no_documents: str="",

The default parameter allow the component to run even if the pipeline don't go through this no_documents branch!

Describe the solution you'd like
Could it be possible to get a warning/message at runtime or creation of the pipeline when a component that should be run cannot because it will never have its requested value? ( because of a CondionalRouter for example)

Describe alternatives you've considered
A clear and concise description of any alternative solutions or features you've considered.

Additional context
Add any other context or screenshots about the feature request here.