Flow, Add Row to Google Sheets - Error: action does not return data so output will always be NULL

Shopify Plus

Topic summary

A user encountered a confusing “NULL output” error when using Shopify Flow’s “Add Row to Google Sheets” action to populate product handles and titles into a spreadsheet with pre-filled ID numbers.

The Issue:

  • The workflow completed without errors, but no data appeared in the expected location
  • Error message stated the action “does not return data so output will always be NULL”
  • The spreadsheet had 3 columns (Product Handle / Product Title / ID) with the ID column pre-populated

The Resolution:

  • The “Add Row” action appends data after the last existing row, not to the first empty cells in a column
  • Data was actually being written successfully around row 300, where the first completely blank row existed
  • The NULL error message was misleading—it refers to the action’s output variable, not whether data was written

Key Takeaway:
The Google Sheets integration appends new rows at the end of existing data rather than filling gaps in partially populated sheets. Removing pre-filled data or adjusting the workflow design resolves the placement issue.

Summarized with AI on October 30. AI used: claude-sonnet-4-5-20250929.
1

Hi Community

First post newbie here but wish I had signed up sooner.

Have picked up Flow recently and now have working automations for product data and metadata. One of my metadata fields is a unique product ID that I want for easier product identification. There’s probably an easier way to update this field but I ended up using a spreadsheet with 3 columns:

Product.Handle / Product.title / ID

The ‘ID’ column (3rd column) is prepopulated with an incremental ID number and I want to add the product handle and product title in the first two columns.

The workflow comes back as completed without error but no data has been added to the google doc. The add row to google sheets step has picked up the correct values for handle / title from the correct worksheet but the output of the script is NULL with an error message: ‘The action does not return data so the output will always be NULL’

Screenshots are below, any help would be appreciated.

…

This is my workflow and variables in the Add Row to Google step.

MGRNZ_0-1742399415286.png
MGRNZ_0-1742399415286.png1447×628 70 KB

This is my google doc

MGRNZ_1-1742399584488.png
MGRNZ_1-1742399584488.png1162×400 12.2 KB

This is result after a new product was created (Title and handle = ‘Dummy Product’)

MGRNZ_2-1742399793374.png
MGRNZ_2-1742399793374.png1540×720 57 KB

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2

I don’t think you can write to a row that has already been created. This action appends after the last row. So likely it’s doing exactly that. If you see no output, make sure the tab name matches exactly.

3

great thank you that makes sense, I’ll take out the third column and see what happens.

4

You’re correct Paul, it turns out the entries had been made down around row 300 which was where the first blank row was.

Thanks for the easy fix.

1 Like