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[PR #5567] [open-swe] fix: Add node validation for Command goto targets #4525

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opened 2026-02-20 17:50:20 -05:00 by yindo · 0 comments
yindo commented 2026-02-20 17:50:20 -05:00
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Original Pull Request: https://github.com/langchain-ai/langgraph/pull/5567

State: closed
Merged: No

Fixes #5556

Problem

When using a Command with a goto target that does not exist in the graph, users currently receive a cryptic NoneType error instead of a clear validation message.

Solution

Added validation in the attach_node method to check if goto targets exist in the graph before processing Commands. This provides users with a clear, actionable error message when referencing non-existent nodes.

Key Changes

  • Created a validated version of _control_branch that checks node existence
  • Raises InvalidUpdateError with a descriptive message like "Node '{node_name}' does not exist in the graph"
  • Handles both string and sequence goto targets
  • Preserves END as a valid special target
  • Maintains backward compatibility

Example Improvement

Before:

Command(goto="researcher_tool_node")  # Cryptic NoneType error

After:

Command(goto="researcher_tool_node")  # Clear error: "Node 'researcher_tool_node' does not exist in the graph"

Testing

  • All 766 langgraph tests passed
  • Formatting and linting checks successful
  • No regressions introduced

Fixes #ISSUE_NUMBER

**Original Pull Request:** https://github.com/langchain-ai/langgraph/pull/5567 **State:** closed **Merged:** No --- Fixes #5556 ## Problem When using a `Command` with a `goto` target that does not exist in the graph, users currently receive a cryptic `NoneType` error instead of a clear validation message. ## Solution Added validation in the `attach_node` method to check if goto targets exist in the graph before processing Commands. This provides users with a clear, actionable error message when referencing non-existent nodes. ### Key Changes - Created a validated version of `_control_branch` that checks node existence - Raises `InvalidUpdateError` with a descriptive message like "Node '{node_name}' does not exist in the graph" - Handles both string and sequence goto targets - Preserves `END` as a valid special target - Maintains backward compatibility ### Example Improvement Before: ```python Command(goto="researcher_tool_node") # Cryptic NoneType error ``` After: ```python Command(goto="researcher_tool_node") # Clear error: "Node 'researcher_tool_node' does not exist in the graph" ``` ## Testing - All 766 langgraph tests passed - Formatting and linting checks successful - No regressions introduced Fixes #ISSUE_NUMBER
yindo added the pull-request label 2026-02-20 17:50:20 -05:00
yindo closed this issue 2026-02-20 17:50:20 -05:00
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Reference: langchain-ai/langgraph#4525
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