{"record":{"id":"7e9ae629c5c073ed","repo":"TheAlgorithms/C-Sharp","slug":"the-path-collection-should-not-be-empty","errorCode":null,"errorMessage":"The path collection should not be empty.","messagePattern":"The path collection should not be empty\\.","errorType":"exception","errorClass":"ArgumentException","httpStatus":null,"severity":"error","filePath":"DataStructures/ScapegoatTree/ScapegoatTree.cs","lineNumber":251,"sourceCode":"    /// <param name=\"value\">New alpha value.</param>\n    public void Tune(double value)\n    {\n        CheckAlpha(value);\n        Alpha = value;\n    }\n\n    /// <summary>\n    /// Searches for a scapegoat node in provided stack.\n    /// </summary>\n    /// <param name=\"path\">Stack instance with nodes, starting with root node.</param>\n    /// <returns>Scapegoat node with its parent node. Parent can be null if scapegoat node is root node.</returns>\n    /// <exception cref=\"ArgumentException\">Thrown if path stack is empty.</exception>\n    /// <exception cref=\"InvalidOperationException\">Thrown if scapegoat wasn't found.</exception>\n    public (Node<TKey>? Parent, Node<TKey> Scapegoat) FindScapegoatInPath(Stack<Node<TKey>> path)\n    {\n        if (path.Count == 0)\n        {\n            throw new ArgumentException(\"The path collection should not be empty.\", nameof(path));\n        }\n\n        var depth = 1;\n\n        while (path.TryPop(out var next))\n        {\n            if (depth > next.GetAlphaHeight(Alpha))\n            {\n                return path.TryPop(out var parent) ? (parent, next) : (null, next);\n            }\n\n            depth++;\n        }\n\n        throw new InvalidOperationException(\"Scapegoat node wasn't found. The tree should be unbalanced.\");\n    }\n\n    private static void CheckAlpha(double alpha)","sourceCodeStart":233,"sourceCodeEnd":269,"githubUrl":"https://github.com/TheAlgorithms/C-Sharp/blob/96e2905cab7bc6b33ac0a34ee5bb82ddccbcbb6c/DataStructures/ScapegoatTree/ScapegoatTree.cs#L233-L269","documentation":"FindScapegoatInPath walks a stack representing the insertion path and finds the first (deepest) ancestor that is unbalanced relative to the alpha weight condition. It requires a non-empty path; an empty stack means there is no path to inspect, so it throws ArgumentException naming `path`.","triggerScenarios":"Calling FindScapegoatInPath with an empty Stack<Node<TKey>>, e.g. after fully draining the path or calling it before any nodes were pushed (such as on an empty tree).","commonSituations":"Calling rebalancing logic on an empty tree, popping the path stack in caller code before passing it, or reusing an already-consumed path stack.","solutions":["Check path.Count > 0 before calling FindScapegoatInPath.","Only invoke rebalancing after a successful Insert that actually pushed the path.","Push the newly inserted node's ancestors onto the stack before searching for the scapegoat."],"exampleFix":"// before\ntree.FindScapegoatInPath(path);\n// after\nif (path.Count == 0) return;\ntree.FindScapegoatInPath(path);","handlingStrategy":"validation","validationCode":"if (path == null || path.Count == 0) return; // or handle empty-tree case","typeGuard":"static bool HasPath<TKey>(Stack<Node<TKey>> path) => path != null && path.Count > 0;","tryCatchPattern":"try { var (parent, scapegoat) = tree.FindScapegoatInPath(path); } catch (ArgumentException) { /* empty path: nothing to balance */ }","preventionTips":["Push the insertion path before searching for a scapegoat.","Don't reuse a path stack after it has been drained.","Skip rebalancing for empty trees."],"tags":["empty-collection","argument-validation","trees"],"backgroundTag":"empty-required-field","analyzedSha":"96e2905cab7bc6b33ac0a34ee5bb82ddccbcbb6c","analyzedAt":"2026-09-13T17:04:01.438Z","contentChangedAt":"2026-09-13T17:04:01.438Z","schemaVersion":2},"datasetVersion":"2026-09-16T04:17:20.429Z"}