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Occurs when a prompt template received missing or invalid input variables.

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Troubleshooting

To resolve this error, you can:
  1. Review your prompt template for correctness. When using f-string formats, ensure proper escaping of curly braces:
    • Use {{ for single braces in f-strings
    • Use {{{{ for double braces in f-strings
  2. When using MessagesPlaceholder components, confirm you’re passing message arrays or message-like objects. If using shorthand tuples, wrap variable names in curly braces like ["placeholder", "{messages}"]
  3. Debug by examining actual inputs to your prompt template by using LangSmith or logging to verify they match expectations
  4. If sourcing prompts from LangChain Prompt Hub, isolate and test the prompt with sample inputs to ensure it functions as intended
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