Pass null String value to Child Flow optional input parameter

[emillion]

When attempting to run a child flow from a parent flow where the string input is null and the child input parameter is an optional string field, the child flow fails to run with the following error:

The input body for trigger 'manual' of type 'Request' did not match its schema definition. Error details: 'Invalid type. Expected String but got Null.'.

I've tried using a Compose step with this formula:

if(empty(triggerOutputs()?['body/NewJobTitle']),null,triggerOutputs()?['body/NewJobTitle'])

And using the Outputs from this Compose in the Run Child Flow step, but this also resulted in the same error.

Separately, when testing the child flow by itself, I can run it manually with empty optional input string parameters with no errors. In some experimenting with the NewJobTitle input parameter (triggerBody()?['text_5'] in the child flow), this particular Condition check:

empty(triggerBody()?['text_5'] is equal to false

works as expected (returns true).

but I discovered that:

triggerBody()?['text_5'] is equal to null

does not work as expected (returns false)

They are logically similar though I know they are not the same. I realize there may be some nuance with data type here (empty vs. null), and I'm wondering if there is some similar experiment I could try at the Parent flow level in a variable or a Compose step. Is there some way to code an "empty String" instead of a "null value" in my flow so that the child flow will run successfully?

Any input would be appreciated. Thanks in advance!

[emillion]

Correction from original post:

empty(triggerBody()?['text_5'] is equal to true  (I wrote false in the original explanation)

works as expected (returns true).

[Radder]

It's an old post but i reckon it's still a valid issue for a lot of users and one of the first hits that popped up for me. When you pass an empty string from your parent trigger input to the child flow you will run into this error even when it's an optional field. To counter this issue, you need to add the null type to the json schema of your child flow trigger. First find your culprit and then make sure you change your "type" to "types". Missing this step will corrupt the parents "run a child flow" action making the field " disappear"... 

After changing the type then add the possible types in an array as shown below. In the case of a field that also takes integers you could add them in the same fashion.

And that's all you need to do to counter the mismatch.

Do keep in mind you always need some sort of null/type validation in the flow to make sure your logic is working with the correct values at the correct time.

[OliverR-82]

Hi @Radder , thanks for that input. That actually seems quite interesting, but I can't seem to find where one would change the JSON schema for the child input trigger. None of the trigger actions seem to allow editing this. You can view the schema via the 'Peek code' option, but you can't edit the code there.

That said, I've just done a quick test to try and reproduce the problem of the topic starter, and I can't reproduce it. I know I faced the same problem in the past, which is why I am subscribed to this topic. But for some reason triggering a child flow with an empty optional input works now. Maybe MS finally fixed this? 🤷‍♂️

[Radder]

hi @OliverR-82 ,

I wish i was fixed but had the issue yesterday so that's why i figured i posted a (possible) fix here. When your working with dynamically added inputs from your trigger that are empty there is no issue at first. So far all good but when using that same value again in the next child flow calling another flow you will notice that the input is set as a null instead of the "" it was before.

But i should have mentioned this fix is only valid when working with http triggers "when a HTTP request is received" where you can define your own schema and also supports the run a child flow. When using the manual input type there is a difference in how the schema and dynamic values operate. HTTP request triggers use a ? when adding dynamic values from your input where manual types doesn't.

Manual trigger input:

vs HTTP

so, the difference is the triggerbody()['text'] vs triggerbody()?['input'] where the ? makes sure its a nullable.

I personally prefer the HTTP version because of the way you can properly rename elements (input instead of text) etc and dont have to worry about optional fields not containing data because of the ? that is added. So it wont break validations etc and most of the time it works just great with pasting it directly in a child flow or action.

If your using manual triggers the only way to fix this issue would be to export the flow and alter the schema in the exported file, saving en reuploading this with the changes.. not a pretty solution.

(and for those struggling with writing your own schema.. the copy paste of the manual triggers works just fine)