Webhook trigger fails when sent a file in multipart/form-data

[pirogoeth]

Describe the bug
Some of my workflows expect to receive multipart/form-data payloads that may contain a mixture of fields and files. When a file is received in a webhook body, the webhook node fails:

TypeError: Cannot set properties of undefined (setting 'file')
    at Webhook.handleFormData (/usr/local/lib/node_modules/n8n/node_modules/n8n-nodes-base/dist/nodes/Webhook/Webhook.node.js:210:55)
    at Object.executeWebhook (/usr/local/lib/node_modules/n8n/dist/WebhookHelpers.js:215:33)
    at /usr/local/lib/node_modules/n8n/dist/TestWebhooks.js:91:37

To Reproduce
Steps to reproduce the behavior:

1. Create a workflow with a single webhook trigger
2. Listen for test event
3. curl -v -X POST https://my.n8n.host/webhook-test/478238f3-8119-4b5d-83ab-fbb48bdbe157 -F [email protected] -F field=sometext

Expected behavior

Expected the following behavior as in 1.20.0:
Stock webhook trigger, binary data option on:

• Fields are dropped from multipart/form-data body
• Files are stored into binary item

Stock webhook trigger, binary data option off:

• Fields are placed into $json.body
• Files are stored into binary item

Environment (please complete the following information):

• OS: Ubuntu 22.04.3
• n8n Version: 1.21.0+
• Node.js Version: 18.18.2
• Database system SQLite
• Operation mode: main

All tested versions were from the docker.n8n.io/n8nio/n8n repository

Additional context

It appears that n8n 1.20.0 is the last version to handle mixed-content multipart/form-data webhooks as expected.

Behavior in 1.21.x/1.22.x/1.23.x:
Stock webhook trigger, binary data option on:

• Fields are dropped from multipart/form-data body
• Files are stored into binary item

Stock webhook trigger, binary data option off:

• ERROR: Cannot set properties of undefined (setting 'file')

[paulmeller]

+1