Need help wit expression to check if field is empty

[CorruptZeus]

I have a list that can have items created when a file is made through a powerapp, but users will also need to manually put in items manually as well. We wanted to keep the created by column visible, but we began running into an issue where items created through the powerapps were always listed as created by whomever created the flow instead of who filled out the form on the powerapp. I am trying to create a "Creator" column that will take the information of who filled out the powerapp and update the "creator" column in the list with that information, but since items can be manually entered as well I need the created by information to be copied over to that column as well so that way we don't have both of the "Creator" and "Created By" columns. 

The problem I need help with is I don't know how to make an expression or function on the Flow to check if the creator column is empty or not before the list item copies over the "created by information". As it works right now the flow from the powerapps creates an item and fills in the "Creator" column with the person who filled out the form, but then since a new item was created in the list the flow that should copy over the "Created By" information for manually created items replaces the "Creator" information from the flow. So I just need the flow to check if that column is empty before putting any information in it.

I apologize if this post is confusing I had a hard time typing it up to explain my issue. Any help is appreciated.

[GeorgiosG]

Hi @CorruptZeus ,

can you make the Created By Column in SharePoint visible in order to see who created it ? 
because I assume that it should work properly if you used the SharePoint connector in PowerApp. 

Are you using patching or an Edit Form to submit data ?

Depending on your structure You can also think about prefill your custom Created field with the current logged in user an make this field in PowerApp Readonly. 
User() is the Function to retrieve the current user. https://docs.microsoft.com/en-us/power-apps/maker/canvas-apps/show-current-user

To make the field read only change the display mode to DisplayMode.View

[CorruptZeus]

I'm using SubmitForm to submit. The form itself comes from another list that is used to fill out a word document, then when the word document is created it creates the item on the list I am having trouble with. The item is created with the name of the file, and an attachment/link to the library with the file so that it is documented and connected, but whenever a user fills out the form on the powerapps it creates an item under my name in the list because I made the flow from the form to the file to the list. I am just trying to get it to show who submitted the form and not my name and to me, since I am very new to powerapps and flows and all of this I figured the easiest way is to just create a new column that carries over this information and updates that on the list since I can't update the "Created by" column through the update file flow. Or at least I can't figure out how to if it is possible.

[GeorgiosG]

Point is that your flow in the background is running under your context. Means that in list two, you always will be inserted as creator. 

You can think about redesigning your three step process to a two step process.

Use a PowerApp (V2) Trigger in PowerAutomate to have the possibility to trigger a Flow from Power App in the context of the logged in user. With that you can Use two actions for your Lists.

With the automated word creation I would work with a separated flow because I assume that you have a premium license for that. You can Trigger the flow when an item is created in list a and do your steps here. 

[CorruptZeus · Accepted solution]

I'm just dumb and forgot that conditional flow steps exist haha, I just made a condition to check if the column is empty then update it if it is, and do nothing if its not empty. It seems to be working the way I was intending it too now though, thanks for the help.