dotnet/reactive · error · InvalidOperationException

Did not find

Error message

Did not find '{xpath}'

What it means

GetRequiredNode is an XmlDocument extension that selects a single node via XPath and throws InvalidOperationException if SelectSingleNode returns null. It exists so tooling can fail fast when an expected element/attribute is missing from an XML document rather than leaking a NullReferenceException later.

Solutions

1. Verify the XPath string against the actual document structure and fix typos/case
2. Handle XML namespaces explicitly (add namespace manager or use local-name() in the XPath)
3. Confirm the source document is the expected version/schema that contains the node

Example fix

// before
var node = doc.GetRequiredNode("/Project/PropertyGroup/TargetFramework");
// after
var node = doc.SelectSingleNode("/Project/PropertyGroup/TargetFramework");
if (node == null) { /* document lacks the element; handle or report clearly */ }

var node = document.SelectSingleNode(xpath);
if (node is null) { Console.WriteLine($"Document lacks node for xpath '{xpath}'"); return; }

bool hasNode = document.SelectSingleNode(xpath) is not null;

try { var n = doc.GetRequiredNode(xpath); }
catch (InvalidOperationException ex) when (ex.Message.StartsWith("Did not find")) { Console.Error.WriteLine($"XML missing expected node: {ex.Message}"); }

When it happens

Trigger: Calling document.GetRequiredNode("/some/xpath") where no node matches the XPath — wrong path spelling, wrong namespace prefix, or the element genuinely absent from the document.

Common situations: Gauntlet build scripts expecting a project-file element (e.g. a property in a .csproj) that was renamed or removed; XML documents with default namespaces where the XPath lacks namespace handling.

Understand the failure class

Background: 'Could not be found', 'does not exist', 'not found in database': the resource-not-found family when an ID, slug, key, or URI lookup comes back empty — this error's family across 20 libraries.

Related errors

• action
• action (Parameter 'action')
• action (Parameter 'action')
• action (Parameter 'action')
• action (Parameter 'action')

AI-assisted analysis of dotnet/reactive@94b5d5ab91 (2026-09-15). Data as JSON: /api/errors/865931e6c34b806c. Report an issue: GitHub.

Appendix: source

Thrown at Rx.NET/Test/Gauntlet/RxGauntlet.Common/Xml/XmlExtensions.cs:14

// Licensed to the .NET Foundation under one or more agreements.
// The .NET Foundation licenses this file to you under the MIT License.
// See the LICENSE file in the project root for more information.

using System.Xml;

namespace RxGauntlet.Xml;

public static class XmlExtensions
{
    public static XmlNode GetRequiredNode(this XmlDocument document, string xpath)
    {
        return document.SelectSingleNode(xpath)
            ?? throw new InvalidOperationException($"Did not find '{xpath}'");
    }

    public static void SetAttribute(this XmlNode node, string attributeName, string attributeValue)
    {
        var attributes = node.Attributes!;
        if (attributes[attributeName] is not XmlAttribute attribute)
        {
            attribute = node.OwnerDocument!.CreateAttribute(attributeName);
            attributes.Append(attribute);
        }

        attribute.Value = attributeValue;
    }
}

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