# Description Nullable reference types are now enabled once, in `common.props`, and every project in the repository builds warning-clean with them. **Configuration** - `<Nullable>enable</Nullable>` lives in `common.props`. All per-project `<Nullable>` settings are removed: 178 project files (enable, annotations, and the `disable` in the three Aot test projects). - 419 per-file `#nullable enable`/`restore` directives and the 4 `#nullable disable` directives are removed. - Kept on purpose: - The 5 `<auto-generated>` schema files (`UANodeSet.cs`, `UA Type Dictionary.cs`, `OPCBinarySchema.cs`, `SecuredApplication.cs`, `PInvokeHelper.cs`) keep `#nullable enable`. The compiler ignores the project setting in generated code, so the directive is required there. - `tests/Opc.Ua.Interop.LegacyPeer` keeps `disable`. It builds against the 1.5.378 packages and does not import the repository props. - `docs/DeveloperGuide.md` and `.github/copilot-instructions.md` now describe the central setting. **Migration** (the 43 unset and 13 annotations-only projects, roughly 10k diagnostics) - **Production code: annotated at the declarations.** Covers `tools/Opc.Ua.SourceGeneration.Core`, `src/Opc.Ua.Lds.Server` and the LDS sample. - Members, parameters and returns are nullable where null actually flows. - Null-check helpers carry `[NotNullWhen]` (`IsNull`, `IsValidXmlName`, `IsMethodTypeDesign`). - `CoreUtils.Format`, `Utils.Format`, `ITemplateWriter.WriteLine` take `params object?[]`. `Template.AddReplacement` takes `string?` (rendering already skips null replacements). - `IRegisteredServerStore.RegisterAsync` returns `Task<RegistrationEntry?>`: it returns null when a registration is removed. - Dereferences backed by an invariant (for example, the validated model) use `!`, so runtime behaviour is unchanged. - **Behavioural changes in production code** (small, deliberate): - `NodeSetToModelDesign` throws `InvalidOperationException` when the file is not a NodeSet. Before, it threw a NullReferenceException on the next line. - `ModelDesignValidator` starts its lookup tables empty instead of null. A redundant `if (m_nodes == null) return;` guard is gone. - **Test code: minimal annotations.** - `?` on values that can be null, `!` where the test asserts non-null. - `= null!` for fixture members assigned in SetUp. - `TryGetStructure<T>(out T? x)` where the inferred `T?` broke the `IEncodeable` constraint. - A few redundant `== null` checks on structs (`NodeId`, `ArrayOf<T>`) folded into the adjacent `IsNull`/`Count` checks. **Notes for reviewers** - The diff is large (~1,500 files) but almost entirely mechanical: `?`, `!` and directive removal. The non-annotation changes are listed above. - Known follow-up, not done here: `IModelDesign.Namespaces/TargetNamespace/NamespaceUris` stay non-nullable even though the validator returns null before it loads a dictionary. Making them nullable would ripple through every generator call site. ## Related Issues - Fixes #4439 ## Checklist - [ ] I have signed the [CLA](https://opcfoundation.org/license/cla/ContributorLicenseAgreementv1.0.pdf) and read the [CONTRIBUTING](https://github.com/OPCFoundation/UA-.NETStandard/blob/master/CONTRIBUTING.md) doc. - [ ] I have added tests that prove my fix is effective or that my feature works and increased code coverage. - [x] I have added all necessary documentation. - [x] I have verified that my changes do not introduce (new) build or analyzer warnings. - [ ] I ran **all** tests locally using the **UA.slnx** solution against at least .net **framework** and .net **10**, and all passed. - [ ] I fixed **all** failing and flaky tests in the CI pipelines and **all** CodeQL warnings. - [ ] I have addressed **all** PR feedback received. The "no new warnings" box covers net10.0 and net48: full non-incremental builds of `UA.slnx`, `tools/SourceGeneration.slnx`, `tools/MigrationAnalyzer.slnx` and the Aot test projects finished with 0 warnings and 0 errors under the repository's warnings-as-errors settings. net9.0 and net8.0 also had no nullable diagnostics, but they were not rebuilt after the final fixes. Tests have not been run locally yet. 🤖 Generated with [Claude Code](https://claude.com/claude-code) --------- Co-authored-by: Claude Opus 5.5 <noreply@anthropic.com>
OPC 10000-110 Asset Management Basics samples
Two console applications that show the Opc.Ua.AMB* libraries end to end: a
server that makes Device Integration devices and a Machinery machine
manageable assets, and a client that finds and reads them with AmbClient.
| Sample | What it does |
|---|---|
| AmbServer | Serves a cooling pump, the flow sensor it relies on and a hydraulic press as assets, and simulates their health alarms and maintenance |
| AmbClient | Discovers every asset, prints a snapshot of each, the location hierarchies, adds and removes a documentation link, and streams health alarms and maintenance activities |
The Asset Management Basics developer guide explains every API used here.
Run
In two terminals:
dotnet run --project samples/AMB/AmbServer -- --port 62553
dotnet run --project samples/AMB/AmbClient -- --insecure --seconds 60
--insecure makes the client accept the server's self-signed certificate;
never use it in production. The client also takes --url <endpoint> (default
opc.tcp://localhost:62553/AmbServer), --seconds <n> (how long to stream,
0 to skip) and --asset-id <id> (writes a new AssetId to the first asset
that has one and finds the asset by it).
The server keeps what clients write - AssetIds, edited and added
documentation links, the writable location and local time - below the local
application data folder (OPC Foundation/AmbServer/state), or in the folder
given with --state <directory>. Stop the server, start it again, and the
client reads the values it wrote before.
What the server shows
| File | Shows |
|---|---|
Program.cs |
AddMachinery() as the owner of the Device Integration address space, AddAssetManagement(...) with UseFileSystemStores, ConfigureAssetManagement(...) defining the location hierarchies and the ECLASS dictionary entry, ConfigureMachinery<T>() and ConfigureDevicesFor<MachineryNodeManager>(...) |
Plant.cs |
Two DI devices registered with RegisterAsAssetAsync: every building block - configurable AssetId, DeviceHealth derived from the alarms, health alarms, maintenance activities with details, documentation links (fixed, editable, user links), version information, locations and local time, classification, requirements and capabilities, and a 0:Utilizes relation between the assets |
PressConfigurator.cs |
A Machinery machine registered through IMachineHandle<T>.AsNode(); its servicing switches the machine into the Maintenance operation mode while it executes |
PlantSimulation.cs |
A BackgroundService that raises and clears a bearing temperature alarm with the sensor as root cause once a minute, fails the self test of the sensor every five minutes (AssetRootCauses.Self), and moves a maintenance activity of the pump and of the press on every two minutes |
Health alarms and maintenance activities are created while the owning node
manager builds its address space, which is why Plant and
PressConfigurator register the assets from the DI and Machinery setup.
What the client shows
Code in Program.cs |
Shows |
|---|---|
connection.Session.AssetManagement(telemetry) |
Creating the client; registers the AMB structured types |
amb.IsSupported |
Detecting whether the server publishes the AMB namespace |
DiscoverAssetsAsync |
All assets from the AMB alias categories |
ReadAssetAsync → AssetSnapshot |
Identification, DeviceHealth, alarms, maintenance, links, locations and classification in one pass |
BrowseLocationsAsync |
The hierarchical and operational location trees and the assets in them |
AddDocumentationLinkAsync, ReadDocumentationLinksAsync, RemoveDocumentationLinkAsync |
The DocumentationLinks AddIn |
WriteAssetIdAsync, FindAssetsAsync |
Configuring an AssetId and finding the asset by it |
ObserveHealthAlarmsAsync, AcknowledgeAsync |
Health alarms with severity, fault category and root causes; a cleared alarm is acknowledged |
ObserveMaintenanceAsync |
Maintenance activities moving through Planned, Executing and Finished |
SampleSession.cs is the session setup. It
keeps the ApplicationInstance alive until the session closes, because the
instance owns the CertificateManager the session validates with, and it
creates a ManagedSession, whose default streaming subscription the observe
calls use.
Troubleshooting
| Symptom | Fix |
|---|---|
Client reports BadCertificateUntrusted |
Pass --insecure for the demo, or trust the server certificate in the client's PKI (under the local application data folder, OPC Foundation/AmbClient/pki) |
AddLink / RemoveLink: refused: BadUserAccessDenied |
The server refuses anonymous link editing unless AuthorizeLinkEdit allows it; the sample server allows it |
| The stream shows nothing for a while | The alarm becomes active 20 s into every minute and maintenance moves on every two minutes; stream longer with --seconds |
| Port already in use | Start the server with --port <n> and the client with --url opc.tcp://localhost:<n>/AmbServer |