{"record":{"id":"2f68dcd6e625245f","repo":"langchain-ai/langgraph","slug":"at-key-self-key-untrackedvalue-guard-true-ca","errorCode":null,"errorMessage":"At key '{self.key}': UntrackedValue(guard=True) can receive only one value per step. Use guard=False if you want to store any one of multiple values.","messagePattern":"At key '(.+?)': UntrackedValue\\(guard=True\\) can receive only one value per step\\. Use guard=False if you want to store any one of multiple values\\.","errorType":"validation","errorClass":"InvalidUpdateError","httpStatus":null,"severity":"error","filePath":"libs/langgraph/langgraph/channels/untracked_value.py","lineNumber":60,"sourceCode":"        \"\"\"Return a copy of the channel.\"\"\"\n        empty = self.__class__(self.typ, self.guard)\n        empty.key = self.key\n        empty.value = self.value\n        return empty\n\n    def checkpoint(self) -> Value | Any:\n        return MISSING\n\n    def from_checkpoint(self, checkpoint: Value) -> Self:\n        empty = self.__class__(self.typ, self.guard)\n        empty.key = self.key\n        return empty\n\n    def update(self, values: Sequence[Value]) -> bool:\n        if len(values) == 0:\n            return False\n        if len(values) != 1 and self.guard:\n            raise InvalidUpdateError(\n                f\"At key '{self.key}': UntrackedValue(guard=True) can receive only one value per step. Use guard=False if you want to store any one of multiple values.\"\n            )\n\n        self.value = values[-1]\n        return True\n\n    def get(self) -> Value:\n        if self.value is MISSING:\n            raise EmptyChannelError()\n        return self.value\n\n    def is_available(self) -> bool:\n        return self.value is not MISSING\n","sourceCodeStart":42,"sourceCodeEnd":74,"githubUrl":"https://github.com/langchain-ai/langgraph/blob/38031739e551638e373fb553453256c23feeb41f/libs/langgraph/langgraph/channels/untracked_value.py#L42-L74","documentation":"Error \"At key '{self.key}': UntrackedValue(guard=True) can receive only one value per step. Use guard=False if you want to store any one of multiple values.\" thrown in langchain-ai/langgraph.","triggerScenarios":"Thrown at libs/langgraph/langgraph/channels/untracked_value.py:60 when the library encounters an invalid state.","commonSituations":"See trigger scenarios.","solutions":[],"exampleFix":null,"handlingStrategy":null,"validationCode":null,"typeGuard":null,"tryCatchPattern":null,"preventionTips":[],"tags":[],"backgroundTag":null,"analyzedSha":"38031739e551638e373fb553453256c23feeb41f","analyzedAt":"2026-08-26T18:02:49.312Z","schemaVersion":2},"datasetVersion":"2026-08-26T21:11:00.512Z"}