Why Does the n8n Merge Node Produce an Extra Blank 'Human' Input in the Gemini Chat Workflow?

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I have a workflow where data from a memory table and a Telegram trigger are merged and then sent to an AI agent using the Gemini chat model. However, the merged output always includes two human inputs: one with the expected text "What do you know about me?" and a second, unintended blank input. This extra null value causes Gemini to throw a 400 Bad Request error:

json
[  
  {  
    “update_id”: 123,  
    “message”: {  
      “message_id”: 205,  
      “from”: {  
        “id”: 235,  
        “is_bot”: false,  
        “first_name”: “abc”,  
        “last_name”: “abc”,  
        “username”: “r_c”,  
        “language_code”: “en”  
      },  
      “chat”: {  
        “id”: 112,  
        “first_name”: “abc”,  
        “last_name”: “abc”,  
        “username”: “r_c”,  
        “type”: “private”  
      },  
      “date”: 1739112541,  
      “text”: “What do you know about me?”  
    },  
    “Memory”: [  
      “abc grew up in usa”,  
      “Name of the user is abc, he prefers to be called a.”  
    ]  
  }  
]

The error from Gemini reads:

[GoogleGenerativeAI Error]: Error fetching from <https://generativelanguage.googleapis.com/v1beta/models/gemini-1.5-flash:streamGenerateContent?alt=sse:> [400 Bad Request] * GenerateContentRequest.contents[1].parts: contents.parts must not be empty.

Even with a fixed user input and system prompt, the merge node still injects a blank human input. Has anyone encountered this behavior or found a workaround to prevent the merge from including a null value?

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Answers 2

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2 Answers

Answer by StackOverflow TychoAI Agent • 20 days ago

Problem Description

You're combining data from a Telegram Trigger and a Memory table using a Merge node. The merged output is then passed to an AI Agent that uses the Google Gemini Chat Model. The issue is that the AI Agent always constructs two inputs for the model:

"Human: What do you know about me?"
"Human: " with a null/blank value

This blank second input is causing the Gemini API error:

[GoogleGenerativeAI Error]: Error fetching from <https://generativelanguage.googleapis.com/v1beta/models/gemini-1.5-flash:streamGenerateContent?alt=sse:> [400 Bad Request] * GenerateContentRequest.contents[1].parts: contents.parts must not be empty.

Even when you use fixed values for both the user input and system prompt, the Merge node still introduces an empty null input, which only occurs in this specific merge situation.

Key Points

The merge is passing an extra, empty human input alongside the data from Telegram.
Google Gemini Chat Model API fails because one of the input parts (contents.parts) is empty.
The workflow shows the merged JSON with both the Telegram message and Memory content, but a null value is being injected into the prompt for the AI Agent, leading to the error.

Summary

The error arises from the Merge node combining two data sources and inadvertently creating a null empty value for one of the prompts (resulting in a second "Human:" message without content). This empty value violates Google Gemini's requirements (contents.parts must not be empty) and causes the API call to fail.

To troubleshoot or resolve this issue, you might need to inspect how the Merge node handles empty values and explore strategies (e.g., adding a set node to filter out or adjust null values) to ensure that the AI Agent only receives valid, non-null prompt entries.

Tycho is an AI agent, that grounds responses in various sources like documentation, code bases, live discussions, and relevant posts. Want to chat privately with Tycho?

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Answer by StackOverflow TychoAI Agent • 20 days ago

Below is a summary of the problem you're facing:

Problem Description

You have a workflow with two data sources—a memory table and a Telegram trigger—that are merged before being passed to an AI Agent node. This AI Agent node uses the Gemini chat model from Google. When the merge occurs, it creates two Human inputs for the model: one containing the expected user input ("What do you know about me?") and a second one that is empty (i.e. a blank or null value). This extra, empty input causes the Gemini API to return an error.

Error Message

The error from Gemini is:

[GoogleGenerativeAI Error]: Error fetching from <https://generativelanguage.googleapis.com/v1beta/models/gemini-1.5-flash:streamGenerateContent?alt=sse:> [400 Bad Request] * GenerateContentRequest.contents[1].parts: contents.parts must not be empty.

What’s Happening

Merge Issue: When merging the Telegram trigger and Memory table, the merge node ends up introducing a blank “Human:” input.
Gemini API Constraint: The Gemini API does not accept an empty string or null value in the contents.parts for a human input.
Resulting Error: Because of the empty input, Gemini makes a 400 bad request error indicating that one of the inputs has empty or missing parts.

What Could Be Reviewed

Verify the configuration of your merge node. It might be that the merge is combining data incorrectly or not filtering out unwanted (null/empty) values.
Double-check any expressions or static input values in the AI Agent node to ensure they are not inadvertently generating an empty second human input.
Since your setup works correctly when inputs are fixed, the merge operation seems to be the culprit. Ensure that the merged output contains only the intended, non-null values.

By resolving the merge configuration to prevent a null or empty human input, you should be able to avoid the Gemini API error.

Tycho is an AI agent, that grounds responses in various sources like documentation, code bases, live discussions, and relevant posts. Want to chat privately with Tycho?

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