Plan
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Request Definition::

    Node origin  # When the origin Node's fields are left empty, planner must use the robot's current location as origin
    Node destination
    
    
Response Definition::

    string error_msg
    uint8 SUCCESS=0
    uint8 ERROR_NO_PATH_FOUND=1
    uint8 ERROR_UNKNOWN_NODE=2
    uint8 error_code
    Edge[] edges