Multiple payload in Gemini output node

[zoubinho]

Situation

I have been experiencing inconsistent output from my Gemini node (regardless of the model) - currently on models/gemini-2.5-flash. n8n self-hosted last version.
The issue resides in the fact that Gemini will runs my query twice: one test “John Doe” (supposingly hardcoded my Google - TBC, not able to find any reference for this), and one my expected response.
Therefore, the output of my node contains 2 runs/payloads (not 2 items in the same payload).

Subsequently, it doesn’t seem that we can prevent this, or use any trick to select the given payload.

And it doesn’t seem that I can control the order of the payloads.

Tests performed, but unsuccessful

• Use a List node to select only the last one since the List node will always use the 1st payload from the previous node (Gemini). And since I can’t control the output payload, it may use my John Doe payload.
• Use the Merge node, but similar to the List node, it merges the content of the same payload.
• Use Code node, but here again, it is using the last payload with using such a code:

// Gemini returns multiple items/runs. Keep only the last one.
const lastItem = items[items.length - 1].json;

// The model's actual structured output is usually in `text` or `content`.
let parsed;
try {
  parsed = JSON.parse(lastItem.text || lastItem.content || JSON.stringify(lastItem));
} catch (e) {
  throw new Error("Could not parse Gemini output: " + e.message);
}

return [{ json: parsed }];

Temporary fix

I managed to fix this, temporarily I assume, by restarting my n8n docker container.
For miraculous reason, the payload, still produces 2 outputs, but my response is not falling into the 1st run, therefore, my workflow can continue.

After some research, I have a javascript to use in a Code node to be tested in the future. I put it here for reference if anyone would be interested to test it.

/**
 * Function node directly after Gemini.
 * Drops runs that don't contain valid JSON (e.g., the "John Doe" preview),
 * and forwards only the parsed JSON when present.
 */

function extractText(payload) {
  // Try common fields the Gemini/LangChain nodes use
  if (typeof payload === 'string') return payload;
  if (typeof payload?.text === 'string') return payload.text;
  if (typeof payload?.content === 'string') return payload.content;
  if (Array.isArray(payload?.content) && typeof payload.content[0]?.text === 'string') return payload.content[0].text;
  if (typeof payload?.response === 'string') return payload.response;
  if (typeof payload?.output === 'string') return payload.output;
  if (typeof payload?.output_text === 'string') return payload.output_text;
  if (payload?.choices?.[0]?.message?.content) return payload.choices[0].message.content;
  if (payload?.generations?.[0]?.text) return payload.generations[0].text;
  return undefined;
}

// In this run, we expect a single item from Gemini
const payload = items[0]?.json ?? {};
const text = extractText(payload);

if (!text || typeof text !== 'string') {
  // Nothing usable in this run → drop it
  return [];
}

// Accept only valid JSON
try {
  const parsed = JSON.parse(text.trim());
  return [{ json: parsed }];
} catch (e) {
  // Not valid JSON → drop first run (e.g. "John Doe")
  return [];
}

If anyone came up with this issue, please provide a response with your testing, as I’m afraid this issue will resurface for me, and I’d like to get to the bottom of it. Thanks

[Erick_Torres]

If the Gemini node receives two items, the sub-node executes twice (once per item). The solution is to ensure that only one item arrives just before Gemini.

Place a Merge before Gemini and connect the two branches to it. If each branch produces one item, use Merge by Position (1:1) to merge fields from Input 1 and 2 into a single item. If any branch can produce multiple items, prefix each branch with a Split in Batches (size = 1) or an Item Lists (pick first/last) to reduce the number to 1 before the Merge.

[zoubinho]

Thanks Erick.
However, this is not the problem: input of Gemini is only 1 message.
From what I gathered, Gemini is generating a dummy request with a John Doe content to test the node (again, for the reason I don’t understand).

Now I have to say that my workflow is now finished and works well on production. I haven’t faced this error yet again.
What I did was to restart my n8n container, and the issue cleared. I’m not entirely sure how was the state of my instance to generate such a glitch, but I’m off the hook for now.