n8n-io/n8n · error · NodeOperationError

A non-empty prompt is required.

Error message

A non-empty prompt is required.

What it means

Thrown in the Gemini 'text / message' operation after the assembled messages array is filtered to those whose content.trim() !== ''. If that filter yields zero messages, there is nothing to send to generateContent, so the node refuses the request with itemIndex context.

Solutions

1. Ensure at least one message role has non-empty content for the item — typically the 'user' message must carry text.
2. If the content is expression-driven, preview the resolved value and fix the reference (e.g. use $json.message ?? $json.text or a fallback string).
3. When using memory/templates, confirm the template interpolates a non-empty variable or provides default text.
4. Filter the input upstream so items with no text don't reach this node.

Example fix

// before — content can resolve to ''
const content = $json.userInput;

// after — guarantee non-empty
const content = ($json.userInput ?? '').trim() || 'Hello';

const messages = /* …built messages… */;
const nonEmpty = messages.filter((m) => m.content.trim() !== '');
if (nonEmpty.length === 0) {
  throw new Error('Refusing to call Gemini: no message has non-empty content');
}

function hasNonEmptyMessage(messages: { content: string }[]): boolean {
  return messages.some((m) => m.content.trim() !== '');
}

When it happens

Trigger: All chat messages resolved to empty/whitespace-only strings: a Chat Trigger with no user text, a memory/prompt template that produced blank content for every role, an expression referencing a field that is undefined for the current item, or a system message only with no user turn.

Common situations: Connected a memory node whose retrieval returned nothing and the prompt template collapsed to empty; referenced $json.missingField in the message content; the trigger payload's text field is genuinely empty for this run.

Related errors

• A non-empty prompt is required.
• A non-empty prompt is required.
• A non-empty prompt is required.
• A non-empty prompt is required.
• A non-empty prompt is required.

AI-assisted analysis of n8n-io/n8n@5ac6606e81 (2026-08-12). Data as JSON: /api/errors/45c94e3090edccde. Report an issue: GitHub.

Appendix: source

Thrown at packages/@n8n/nodes-langchain/nodes/vendors/GoogleGemini/actions/text/message.operation.ts:515

				tools.push({
					fileSearch: {
						...(fileSearchStoreNames && { fileSearchStoreNames }),
						...(metadataFilter && { metadataFilter }),
					},
				});
			}

			if (builtInTools.codeExecution) {
				tools.push({
					codeExecution: {},
				});
			}
		}
	}

	const nonEmptyMessages = messages.filter((m) => m.content.trim() !== '');
	if (!nonEmptyMessages.length) {
		throw new NodeOperationError(this.getNode(), 'A non-empty prompt is required.', {
			itemIndex: i,
		});
	}
	const contents: Content[] = nonEmptyMessages.map((m) => ({
		parts: [{ text: m.content }],
		role: m.role,
	}));
	const body: GenerateContentRequest = {
		tools,
		contents,
		generationConfig,
		systemInstruction: options.systemMessage
			? { parts: [{ text: options.systemMessage }] }
			: undefined,
		...(toolConfig && { toolConfig }),
	};

	let response = (await apiRequest.call(this, 'POST', `/v1beta/${model}:generateContent`, {

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