- Add #nullable enable to 50 source files
- State machine files: use !. for required mandatory state properties
- ConditionState/AlarmConditionState/etc: nullable annotations on backing fields
- FiniteStateMachineState: nullable parameters for state/transition variables
- Types files (ContentFilter/MonitoringFilter/etc): nullable result classes
- Validate methods returning ServiceResult? when null=success
- ToString IFormattable signature with nullable params
- Timer fields and TimerCallback parameters made nullable

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

- Add #nullable enable to ~107 of 187 source files in Opc.Ua.Types
- Apply nullable annotations to interface signatures (IDecoder, IEncoder, IType)
- Fix override Equals/CompareTo/IFormattable.ToString signatures
- Make IDecoder.ReadString/Array methods return nullable to match implementations
- IEnumeratedType.TryGetSymbol/IEncoder.WriteSwitchField use nullable out string
- Fix Polyfills attributes for nullable awareness
- Fix EnumValueTests for nullable IEnumeratedType signature
- Fix MonitoredItem.cs for nullable EventFieldList.Message

Note: ~80 complex files (BinaryEncoder, NodeState, etc.) remain to be migrated
in a future commit. Project builds clean.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Update Read/Write methods to accept string? fieldName since arrays
and internal callers pass null. Update JsonEncoder/JsonDecoder
implementations to match. Returns also nullable for ReadString/
ReadDataValue/ReadDiagnosticInfo to match JsonDecoder behavior.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

- Add #nullable enable to BuiltIn/Argument, RelativePath, Schema, etc.
- Make IEncodable.IsEqual accept nullable IEncodeable
- Make IEncoder Read/Write methods accept string? fieldName
- Make IEncoder.WriteString/DataValue/DiagnosticInfo/Encodeable values nullable
- Make IDecoder.Read* return types nullable to match implementations
- Make class operator==/!= accept nullable for proper consumer use
- Fix Argument operator== to use direct null check instead of EqualityComparer
- Fix downstream NodeCache.cs to use 'is null' for ReferenceDescription comparison
- Fix Subscription.cs to use null-forgiving on monitoredItem.RelativePath

Progress: 117/187 Opc.Ua.Types files now nullable enabled.
70 complex files (Encoders, NodeState, Variant, etc.) remain.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

- Add nullable to BuiltIn types: BrowseDescription, ViewDescription, EnumDefinition, EnumField,
  EnumValueType, RelativePath, RelativePathFormatter, RolePermissionType, StructureDefinition,
  StructureField, ReferenceDescription, RelativePathElement
- Add nullable to State files: NodeStateFactory
- Add nullable to Utils files: ServiceMessageContext, ServiceResultException, etc.
- Add nullable to Encoders: EncodableObject, Enumeration
- Make DataValue operator==/!= accept nullable
- Replace EqualityComparer<T>.Default.Equals with manual null check in operators
- Fix downstream callers in Stack/Opc.Ua and Encoders/JsonDecoder.cs

Remaining: 54 complex files (BinaryEncoder, BinaryDecoder, NodeState, Variant, etc.)
require deeper changes and have ~2700 errors to address.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

- Add #nullable enable to ~49 files in Opc.Ua.Core that build clean
- Apply bulk fixes: ToString IFormattable signatures, Equals object override
- Make encoder Read/Write methods accept string? fieldName
- Make class operator==/!= accept nullable for class types
- Replace EqualityComparer<T>.Default.Equals in operators with manual null check
- Fix ClientBase.MessageContext to use null-forgiving (! operator)
- Fix TraceLoggerProvider to handle nullable Exception parameter
- Fix Session.cs and HttpsTransportListener.cs downstream callers

Remaining: 81 complex files in Opc.Ua.Core (TcpTransportListener, ApplicationConfiguration,
DirectoryCertificateStore, etc.) still require deeper migration.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

ClientBase.Endpoint, EndpointConfiguration, NullableTransportChannel: Use !
to match IClientBase interface (non-nullable returns). The properties throw
ServiceResultException if the channel is in a bad state, otherwise consumers
can rely on non-null returns.

Also adds #nullable enable to IClientBase.cs.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

- Add #nullable enable directive
- Update method signatures to match IEncoder (string? fieldName)
- Make m_namespaceMappings and m_serverMappings nullable fields
- Use null-forgiving for generic WriteEncodeable internal calls
- Make CloseAndReturnBuffer return byte[]?
- Throw InvalidOperationException in CloseAndReturnText if not MemoryStream
- WriteSwitchField fieldName is out string? per interface

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

- Stack/Opc.Ua.Types/State/ISystemContext.cs
- Stack/Opc.Ua.Types/State/NodeBrowser.cs
- Stack/Opc.Ua.Types/State/BaseDataVariableState.cs
- Stack/Opc.Ua.Types/State/BaseObjectState.cs
- Stack/Opc.Ua.Types/State/DataTypeState.cs
- Stack/Opc.Ua.Types/Nodes/IOperationContext.cs

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

- Stack/Opc.Ua.Types/State/BaseTypeState.cs
- Stack/Opc.Ua.Types/State/ReferenceTypeState.cs
- Stack/Opc.Ua.Types/State/ViewState.cs

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

- Add #nullable enable directive
- Update method signatures to match IDecoder (string? fieldName)
- Make m_namespaceMappings and m_serverMappings nullable fields
- Make ReadString return string? to match interface
- Make ReadDataValue and ReadDiagnosticInfo return nullable types
- Update ReadStringArray, ReadDataValueArray, ReadDiagnosticInfoArray to return ArrayOf<T?>
- Use null-forgiving for generic ReadEncodeable internal calls
- Suppress CS8620 for Variant.From with nullable element ArrayOf
- Make CallerMemberName functionName parameters nullable

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

- Add #nullable enable directive
- Update method signatures to match IEncoder (string? fieldName)
- Make m_root, m_destination, m_namespaceMappings, m_serverMappings nullable
- BeginField helper now accepts string? fieldName
- WriteString, WriteDataValue, WriteDiagnosticInfo accept nullable values
- Throw InvalidOperationException in CloseAndReturnText if no destination
- WriteSwitchField fieldName is out string? per interface

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

- Utils/CoreUtils.cs
- Utils/NamespaceTable.cs
- Utils/ServiceResult.cs
- Utils/Buffers/ArrayPoolBufferWriter{T}.cs
- Utils/FileSystem/VirtualFileSystem.cs
- BuiltIn/AmbientMessageContext.cs
- BuiltIn/EnumHelper.cs
- BuiltIn/ITranslatableObject.cs

Plus minor downstream fixes for nullability of ServiceResult properties
and EnumHelper return types in EnumValue.cs, EncodeableFactory.cs, and
ServiceResultException.cs.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

- Add #nullable enable directive
- Update method signatures to match IDecoder (string? fieldName)
- Make m_namespaceMappings, m_serverMappings nullable
- Make ReadString return string? to match interface
- Make ReadDataValue and ReadDiagnosticInfo return nullable types
- Update ReadStringArray, ReadDataValueArray, ReadDiagnosticInfoArray return types
- Make Peek return XmlQualifiedName?
- Suppress CS8620 for Variant.From with nullable element ArrayOf
- Make CallerMemberName functionName parameters nullable
- Update CreateBadDecodingError and SafeXmlConvert to accept nullable parameters

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Annotates DataValue, ExtensionObject, Matrix, DataContractSurrogates, and EqualityComparers with nullable reference types. Updates the corresponding Equals overloads, IFormattable.ToString signatures, IEquatable<T> contracts, IEqualityComparer<T> contracts, and operator == / != to use nullable parameters where the runtime can be null. Also fixes a downstream consumer in EncodableObject.cs that calls TryGetEncodeable.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

- Add #nullable enable directive
- Update method signatures to match IDecoder (string? fieldName)
- Make m_namespaceMappings, m_serverMappings nullable
- Make ReadString return string? to match interface
- Make ReadDataValue and ReadDiagnosticInfo return nullable types
- Update ReadStringArray, ReadDataValueArray, ReadDiagnosticInfoArray return types
- Make Peek return XmlQualifiedName?
- Make ElementContext.Element nullable
- Suppress CS8620 for Variant.From with nullable element ArrayOf/MatrixOf
- Make CallerMemberName functionName parameters nullable
- Update CreateBadDecodingError and SafeXmlConvert to accept nullable parameters
- Use null-forgiving for TypeInfo.GetXmlName results

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

- UANodeSet.cs: add nullable annotations to auto-generated XML serialization classes
- UANodeSetHelpers.cs: enable nullable, update method signatures for nullable inputs
- BinarySchemaValidator.cs: enable nullable, accept nullable string params
- OPCBinarySchema.cs: add nullable annotations to auto-generated XML schema classes
- SchemaValidator.cs: enable nullable, accept nullable params for Load and Exception helpers
- TypeDictionaryValidator.cs: enable nullable, handle nullable schema properties
- UA Type Dictionary.cs: add nullable annotations to auto-generated XML classes
- XmlSchemaValidator.cs: enable nullable, accept nullable typeName/file params
- XmlSchemaValidator2.cs: enable nullable, accept nullable typeName/file params

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

…StateCollection.cs

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

- Use null-forgiving for xml after string.IsNullOrEmpty checks (older targets)
- Use default! for EqualityComparer<T>.Default.Equals in BinaryEncoder
- Use null-forgiving for TypeInfo.GetXmlName results
- Add null coalescing for fieldName in error messages
- Suppress CS8604 for Variant.From with nullable DataValue

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

After enabling #nullable on 52 files in Stack/Opc.Ua.Types, downstream
projects had build errors due to stricter nullability annotations
flowing through interfaces. This commit fixes those errors so the full
solution builds cleanly.

Stack/Opc.Ua.Types fixes:
- JsonDecoder.cs: nullable string handling in namespace/server URI
  loops, suppression of generic variance for Variant.From overloads
  taking ArrayOf/MatrixOf with nullable elements
- JsonEncoder.cs: nullable handling for TryGetEncodeable/TryGetAsJson/
  SymbolicId
- BuiltInType.Obsolete.cs, QualifiedName.cs, RelativePathFormatter.cs,
  ReferenceDescription.cs, BaseInstanceState.cs: standard nullable
  annotation/suppression patterns

Stack/Opc.Ua, Stack/Opc.Ua.Core fixes:
- ContentFilter.cs, MonitoringFilter.cs, NotificationMessage.cs,
  AlarmConditionState.cs, DialogConditionState.cs, AuditEventState.cs,
  FiniteStateMachineState.cs, HistoryReadValueId.cs, ReadValueId.cs,
  WriteValue.cs: nullable annotations for INode?, out parameters from
  TryGetEncodeable, NumericRange.Parse non-null arguments
- ClientBase.cs, ServiceResultExtensions.cs,
  SecuredApplicationEncoding.cs: matching nullable annotations

Libraries/Opc.Ua.Client fixes:
- ComplexTypeSystem.cs, DataTypeDefinitionExtension.cs, NodeCache.cs,
  NodeCacheContext.cs, Session.cs, SessionClientBatched.cs,
  SessionClientExtensions.cs, SessionConfiguration.cs, Browser.cs,
  MonitoredItemStatus.cs, Subscription.cs: same patterns

Applications/McpServer fixes:
- OpcUaJsonHelper.cs, AttributeServiceTools.cs, ConvenienceTools.cs,
  NodeSetExportTools.cs: same patterns

Tests fixes:
- EnumHelperTests.cs, ServiceResultTests.cs, ClientBaseTests.cs:
  match new nullable signatures

Source generator fix:
- ObjectTypeProxyTemplates.cs: emit pragma to suppress CS8600 in
  generated TryGetStructure call sites where the analyzer ignores
  MaybeNullWhen(false) annotations

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

After enabling nullable end-to-end, several downstream errors surfaced:

- MonitoredItem ctor (Opc.Ua.Server): widened originalFilter, filterToUse,
  range parameters to nullable. The ctor body already handled null for
  these (Filter/m_filterToUse fields are nullable; range null-checked at
  line 141; originalFilter is-pattern at 117). MemoryBufferMonitoredItem
  and other derived-class ctor calls now compile cleanly.

- DataChangeMonitoredItem.OnReportValueChange: added ! to value/error
  arguments passed to MonitoredItem.ValueChanged (static method has
  non-null params; the surrounding code already checks if value != null
  on the immediately-following line so the call path is non-null in
  practice). Same for m_queue?.QueueValue(value!, error!).

- TestDataNodeManager/AlarmNodeManager: NodeState source = ValidateNode(...)
  -> NodeState? source (CustomNodeManager.ValidateNode now returns NodeState?
  after the prior commit; downstream callers in Quickstarts.Servers needed
  the same change as the Opc.Ua.Server callers).

- TestDataNodeManager:207: conditionsFolder!.AddNotifier(...) — the
  FindPredefinedNode<NodeState> returns nullable; current behavior NREs
  on null, ! preserves that runtime behavior while satisfying the compiler.

- MemoryBufferMonitoredItem.Modify: ! on ModifyAttributes return — the
  base method now returns ServiceResult? (nullable) but Modify declares
  ServiceResult; preserves prior behavior (was returning a non-null
  result from a nullable signature already).

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

…eMonitoredItem

After widening m_filterToUse to nullable in commit cc8943d, two
diagnostic-helper call sites (ServerUtils.ReportCreateMonitoredItem in
both ctors) flagged CS8604 because the helper expects non-null filter.
Same pattern used at lines 729 and 817 in commit 7e2f415 - add !
preserves the prior runtime behavior (the diagnostic helper handles
null at runtime; the static signature is overly strict).

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

The test project links Applications/ConsoleReferenceClient/ClientSamples.cs
as a Compile-Item (line 30 of csproj). After enabling nullable on
ConsoleReferenceClient (commit a4d9487), the linked file gained ?
annotations that fail with CS8632 in the test project's compile context.

Setting <Nullable>annotations</Nullable> enables annotation PARSING
without enforcing nullable analysis on the rest of the test code —
minimal change that resolves the CS8632 errors without requiring a
full Tests/ migration (which is out of scope for this PR).

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

CI test failures showed the server failing to start with InvalidOperationException
in ServerSystemContext.get_OperationContext, called via Copy from DiagnosticsNodeManager.CreateAddressSpaceAsync.

Commit a4d9487 changed the getter from null-silent return (with a meaningless !)
to throw. This was a runtime behavior change: callers were already handling
null returns (CustomNodeManager.cs:3252 has 'OperationContext != null' guard).
Throwing breaks startup because DiagnosticsNodeManager runs before any
operation has been issued and Copy propagates null via line 172.

Restored original null-returning behavior; now declares return type as
OperationContext? to match reality. All current call sites already handle null.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

…e revert

Reverting OperationContext getter to nullable (commit 1d9df71) cascaded
8 new CS8604 errors at sites that pass it to non-null param contracts. All
are in 'normal operation' code paths (after session/operation has begun)
where OperationContext is invariably non-null in practice; preserved with !.

Fixed sites:
 - DiagnosticsNodeManager.cs:316 (ResendData),:495 (ConditionRefresh),:513 (ConditionRefresh2)
 - MonitoredNode.cs:262 (capture from serverSystemContextToUse), :355 (cachedEntry.Context)
 - SamplingGroupMonitoredItemManager.cs:95 (CreateMonitoredItem),:195 (ModifyMonitoredItem)

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Remove unresolved 'ISystemContext.OperationContext' cref in XML doc remark
that prevented Opc.Ua.Server from building (the type lives in Opc.Ua,
not Opc.Ua.Server, and the simple cref form failed to resolve).

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

… nullable

Add ! after .OperationContext (now nullable). The Quickstarts SampleNodeManager
diagnostic-info path here does not pre-check OperationContext for null
(unlike CustomNodeManager.cs:3252 which does); preserved prior runtime
behavior with !.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

The ComponentCache lookup had inverted TryGetValue checks that caused
NRE on first cache hit and silently returned null after AddNodeToComponentCache:

    if (!m_componentCache.TryGetValue(handle.RootId, out entry))   // BUG: when NOT found
    {
        return entry!.Entry!.FindChildBySymbolicName(...);    // entry is null here
    }

The ! inversions look like collateral damage from the bulk Server migration
script (commit 245e92b) that flipped many == to != in nullable-related
guards; later cleanup (1988bca, 1581531) caught most but missed these.
Matches the AddNodeToComponentCache pattern (which uses positive TryGetValue).

Fixes test failures: TestComponentCacheAsync, AddNodeToComponentCacheFirstAddCreatesEntry,
AddNodeToComponentCacheSecondAddIncrementsRefCountAndReturnsCachedNode,
AddNodeToComponentCacheWithComponentPath* and others. Also explains the
downstream Server startup InvalidOperationException seen in earlier CI runs
because AsyncCustomNodeManager.DeleteNodeAsync indirectly walked the cache.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

…NodeInComponentCache (matches commit deb49de fix)

…FindMethodInTypeHierarchy

1. MasterNodeManager.ValidateRolePermissions: lines 3955/3960 had inverted IsEmpty checks.
   Comments inside the branches said 'there were no role permissions defined for this node'
   but the conditions were checking '!IsEmpty'. Removed the ! so the logic matches the comments.
   Fixes: ValidateRolePermissions_DefaultPermissions_ReturnsGood (and 4 sibling tests).

2. CustomNodeManager.cs:3148, AsyncCustomNodeManager.cs:3302: the per-spec ObjectType-method
   resolution path declared a NEW local 'MethodState? method2 = FindMethodInTypeHierarchy(...)'
   instead of assigning to the outer 'method' variable that the next 'if (method == null)' check
   uses. The result of the type-hierarchy lookup was discarded, so any method call on an Object
   instance whose method lives on its ObjectType returned BadMethodInvalid.
   Fixes: CallAsync_InvokesMethodFromObjectTypeAsync, CallAsync_InvokesMethodFromSuperTypeOfObjectTypeAsync.

Both bugs were collateral damage from the bulk Server migration script (245e92b) and not
caught by the prior cleanup commits (1988bca / 1581531).

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Sites only flagged in the Release build / net472 (not Debug/net10.0):

 - MasterNodeManager.cs:1716: context.Session is nullable; ! at use site.
 - ConsoleReferenceSubscriber/Program.cs:249,255,282,292,298: dataSet.Fields,
   dataSet, and DataSetMetaData are nullable per Opc.Ua.PubSub migration.
   Added ! at deref sites (sample-app code path is exercised only with
   real metadata messages).
 - ConsoleReferencePublisher/PublishedValuesWrites.cs:352,356:
   IUaPubSubDataStore.ReadPublishedDataItem now returns DataValue?
   (key-not-found path); changed local to DataValue? and added explicit
   null check before dereferencing WrappedValue.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

The line was 'context.Session!.SaveContinuationPoint(currentCp);' but
'context' itself is nullable in this method (other use sites at lines
1665, 1686 use 'context!'). The ! after Session doesn't help when
context.* is the first deref. Added ! after context too.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Documents the ~3,810 ! operators remaining after the nullable migration,
clustered into 15 root-cause groups with removal strategies, effort
estimates, and a 6-PR follow-up roadmap. Also flags 2 latent (expr as T)!
bug candidates in Opc.Ua.PubSub/Encoding/PubSubJsonDecoder.cs:928,1293.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Replace 15 `= null!;` initializers on auto-properties in PubSub
EventArgs and DTO classes with the C# 11 `required` modifier.
The repo's Stack/Opc.Ua.Types already provides PolySharp-generated
RequiredMemberAttribute polyfills for older TFMs (net472/48/standard2.1)
so this works across all 6 target frameworks without adding new compat
code.

Modified EventArgs (1 prop each):
 ConnectionEventArgs, DataSetReaderEventArgs, DataSetWriterEventArgs,
 ExtensionFieldEventArgs, PubSubStateChangedEventArgs,
 PublishedDataSetEventArgs, ReaderGroupEventArgs, WriterGroupEventArgs

Multi-property classes converted:
 ConfigurationUpdatingEventArgs (Parent, NewValue)
 RawDataReceivedEventArgs (Message, Source, PubSubConnectionConfiguration)
 DataSetWriterConfigurationResponse (DataSetWriterIds, StatusCodes;
   DataSetWriterConfig left as null! since it is conditionally set)

Caller fix:
 UaPubSubConnection.GetDataSetWriterDiscoveryResponses refactored from
 post-construction property assignment to object-initializer syntax to
 satisfy the required-property contract; preserved the conditional
 DataSetWriterConfig=null on not-found path (no runtime change).

Test updates: 5 tests updated to provide initializers for now-required
properties (Message=[], Source=string.Empty, etc.).

Skipped: EventArgs whose properties have `internal set;` (populated by
framework code, not callers) — keeping `= null!;` is correct there.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

…Server

Added 10 [MemberNotNull] attributes across 5 files documenting which
late-init fields each lifecycle method populates. The compiler now
verifies these methods set the fields, eliminating the need for !
operators at downstream use sites.

ServerInternalData.cs (9 attributes, 21 member refs):
 SetNodeManager, SetMainNodeManagerFactory, CreateServerObjectAsync,
 SetSessionManager, SetMonitoredItemQueueFactory, SetSubscriptionStore,
 SetAggregateManager, SetModellingRulesManager

Session.UpdateUserIdentity (1 attribute, 2 member refs):
 EffectiveIdentity, IdentityToken

Use-site eliminations (5 ! removed):
 CustomNodeManager.cs:4972  Server!.NodeManager!  ->  Server.NodeManager
 AsyncCustomNodeManager.cs:5162  same pattern
 StandardServer.cs:3700  ServerInternal.ServerObject!  ->  .ServerObject

The = null!; initializers were preserved because constructors do not call
the lifecycle methods (compiler still requires the suppressor); the
attributes formally document the contract that flow analysis can use
inside any caller that has invoked the lifecycle method.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

…g fixes

A) Two latent (expr as T)! cast bug fixes in PubSubJsonDecoder.cs:
   - Line 928: (serverUriToken as string)! -> (string)serverUriToken (clean
     InvalidCastException instead of swallowed-then-NRE in ToServerIndex).
   - Line 1293: (array.Value as Array)! -> 'is not Array arrayValue' pattern
     match with descriptive ServiceResultException(BadDecodingError).

B) ArraySegmentExtensions.GetArray() helper + bulk migration:
   New internal extension Stack/Opc.Ua.Core/Utils/ArraySegmentExtensions.cs
   with Debug.Assert + AggressiveInlining. Replaced 61 sites of
   ArraySegment.Array! with .GetArray() across 9 files in Opc.Ua.Core
   (BufferManager, ArraySegmentStream, CryptoUtils, EncryptedSecret,
   RsaUtils, UaSCBinaryChannel + Asymmetric/Rsa/Symmetric).

C) ToArray()!.Cast<T> -> .ToList().OfType<T> in JsonDecoder.cs at lines
   3937 and 3941 (NamespaceTable/StringTable construction). ToList yields
   non-null List<string?>, OfType filters nulls and yields IEnumerable<string>
   matching the consumer signature.

Total: ~68 ! operators eliminated, 2 latent bugs fixed.
Build: Opc.Ua.Core, Opc.Ua.PubSub, Opc.Ua.Types all succeed (0 warnings).

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Part A (Dispose-time field cleanup):
 Only Nonce.cs.m_ecdh qualified for safe conversion (already declared
 ECDiffieHellman?; just changed Dispose-line null! to null). All other
 candidate sites (BinaryEncoder/Decoder, XmlDecoder, PubSubJson*,
 BaseComplexType, MonitoredItem, PooledBuffer, ArraySegmentStream,
 TcpTransportListener) were rejected by the conservative criteria
 because their fields are widely accessed without null checks; making
 them nullable would require new null guards (a runtime behavior change).

Part B (Type.GetElementType()! pattern replacement):
 15 sites converted from .GetElementType()! to either 'is Type x'
 pattern matching (compile-time non-null narrowing, no exception path)
 or '?? throw InvalidOperationException' for assignment cases.

 Files (sites):
   Stack/Opc.Ua.Types/BuiltIn/EnumValue.cs (2)
   Stack/Opc.Ua.Types/BuiltIn/TypeInfo.cs (3)
   Stack/Opc.Ua.Types/BuiltIn/VariantHelper.cs (1)
   Stack/Opc.Ua.Types/BuiltIn/Matrix.cs (3)
   Libraries/Opc.Ua.Client.ComplexTypes/Types/ComplexTypePropertyInfo.cs (3)
   Libraries/Opc.Ua.PubSub/Encoding/PubSubJsonEncoder.cs (3)

Total: 16 ! operators eliminated. Builds clean (Types/Core/PubSub all
0 warnings; pre-existing baseline errors in MonitoredNode/SessionExtensions
unrelated to this change).

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Make `string fieldName` parameter nullable across all encoder/decoder
APIs. In binary encoding fieldName is unused (positional encoding) and
callers were universally passing `null!`; making the parameter nullable
eliminates the ! at every call site.

Interface changes (10 methods each):
 IEncoder.cs: WriteEncodeable*, WriteEnumerated*, WriteEncodeableArray*,
   WriteEncodeableArrayAsExtensionObjects, WriteEncodeableMatrix*
 IDecoder.cs: ReadEncodeable*, ReadEnumerated*, ReadEncodeableArray*,
   ReadEncodeableMatrix, ReadEncodeableArrayAsExtensionObjects,
   ReadVariantValue

Implementations updated: BinaryEncoder/Decoder, XmlEncoder/Decoder,
XmlParser (private helper), JsonEncoder/Decoder — 72 method signatures total.

AuditEvent.Initialize source parameter:
 BaseEventState.Initialize and AuditEventState.Initialize: NodeState source
 -> NodeState? source. Eliminates ! at 25 call sites in AuditEvents.cs (×17+3),
 Subscription.cs (×2), MonitoredItem.cs, CustomNodeManager.cs (×3).

Call-site replacements (88 total):
 - 63 IEncoder/IDecoder null! -> null sites
 - 25 e.Initialize(ctx, null!, ...) -> e.Initialize(ctx, null, ...)

Source-breaking note:
 The interface ? annotations on fieldName are source-breaking for
 downstream consumers with NRT enabled — they will see new warnings
 when overriding/implementing the interfaces. Binary-compatible.

Builds: Types/Core/PubSub all 0 warnings. Server/Client have only the
pre-existing `unions` baseline errors (verified via git stash).

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

# Conflicts:
#	Libraries/Opc.Ua.Client/Browser.cs
#	Libraries/Opc.Ua.Client/ComplexTypes/NodeCacheResolver.cs
#	Libraries/Opc.Ua.Client/NodeCache/LruNodeCache.cs
#	Libraries/Opc.Ua.Client/NodeCache/NodeCache.cs
#	Libraries/Opc.Ua.Client/NodeCache/NodeCacheObsolete.cs
#	Libraries/Opc.Ua.Client/Session/DefaultSessionFactory.cs
#	Libraries/Opc.Ua.Client/Session/Session.cs
#	Libraries/Opc.Ua.Client/Session/SessionObsolete.cs
#	Libraries/Opc.Ua.Client/Subscription/MonitoredItem.cs
#	Libraries/Opc.Ua.Client/Subscription/Subscription.cs
#	Libraries/Opc.Ua.Server/Fluent/NodeManagerBuilder.cs
#	Stack/Opc.Ua.Core/Security/Constants/AdditionalParameterNames.cs
#	Stack/Opc.Ua.Core/Security/Constants/SecurityPolicies.cs
#	Stack/Opc.Ua.Core/Security/Constants/SecurityPolicyInfo.cs
#	Stack/Opc.Ua.Core/Stack/Client/DiscoveryClient.cs
#	Stack/Opc.Ua.Core/Stack/Tcp/TcpTransportListener.cs
#	Stack/Opc.Ua.Core/Stack/Tcp/UaSCBinaryChannel.Asymmetric.cs
#	Stack/Opc.Ua.Core/Stack/Tcp/UaSCBinaryChannel.Rsa.cs
#	Stack/Opc.Ua.Core/Stack/Tcp/UaSCBinaryChannel.Symmetric.cs
#	Stack/Opc.Ua.Core/Stack/Tcp/UaSCBinaryClientChannel.cs
#	Stack/Opc.Ua.Core/Stack/Transport/NullChannel.cs
#	Stack/Opc.Ua.Core/Stack/Types/X509IdentityTokenHandler.cs
#	Stack/Opc.Ua.Types/BuiltIn/DataContractSurrogates.cs
#	Stack/Opc.Ua.Types/BuiltIn/ExtensionObject.cs
#	Stack/Opc.Ua.Types/BuiltIn/Variant.cs

After merging master (PR #3730), 3 test sites still passed null as the
first arg to the 2-arg ConfiguredEndpoint(ConfiguredEndpointCollection,
EndpointDescription) ctor whose collection param is non-nullable. The
3-arg overload with nullable collection was already used in production
code (DefaultServerRedundancyHandler, ManagedSessionBuilder); apply the
same pattern in tests by adding 'configuration: null' to disambiguate
to the 3-arg overload.

Files:
 Tests/Opc.Ua.Client.Tests/ClientBuilder/ManagedSessionBuilderTests.cs:54
 Tests/Opc.Ua.Client.Tests/ClientBuilder/OpcUaClientServiceCollectionExtensionsTests.cs:44
 Tests/Opc.Ua.Client.Tests/Session/ServerRedundancyHandlerTests.cs:375

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

After the master merge (Certificate Manager PR #3688) re-introduced
existing test files that pass null to APIs in Opc.Ua.Types which the
nullable migration had not yet annotated. The APIs already handle null
internally (via if-null guards or throw); just need the parameter
annotation to match the existing runtime contract.

Widened params (all already null-tolerant):
 - EnumHelper.EnumArrayToInt32Array(Array values)  -> (Array? values)
 - EnumHelper.EnumArrayToInt32Matrix(Array values) -> (Array? values)
 - RelativePath.IsEmpty(RelativePath relativePath) -> (RelativePath? relativePath)
 - RelativePath.Parse(string, ITypeTable typeTree) -> (string, ITypeTable? typeTree)
 - RelativePath.Parse(string, ITypeTable, NamespaceTable, NamespaceTable) -> (string, ITypeTable?, NamespaceTable, NamespaceTable)
 - ServiceResultException.Create(StatusCode, string format, params)  -> (StatusCode, string? format, params)
 - ServiceResultException.Create(StatusCode, Exception, string format, params) -> (StatusCode, Exception, string? format, params)

Fixes 8 CS8625 errors in Tests/Opc.Ua.Types.Tests that cascade-cancelled
~20 dependent test jobs. No runtime behavior change.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Split the long inline justification comment off the #pragma warning
disable line so the line stays within the 120-char limit enforced
by Roslynator's RCS0056 analyzer.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

After the certificate-manager refactor merge, these sites needed
nullable annotations to align with the new Certificate / CertificateManager
API surface:

ApplicationInstance.cs:
 - ctor: NullLogger fallback when telemetry parameter is null (CS8600)
 - CertificateManager property declared nullable (CS8618)
 - ApplicationConfiguration!.CertificateManager (CS8602; never null after ctor)
 - localManager: CertificateManager? (CS8600 in Dispose)
 - CertificateManager!.ValidateAsync (CS8602; checked just above)
 - m_telemetry! when passing to CertificateManagerFactory.Create
 - passwordProvider declared as ICertificatePasswordProvider? at both sites
 - id.SubjectName! in format args (CS8604)

ApplicationConfigurationBuilder.cs:
 - ApplicationConfiguration.ServerConfiguration! (CS8602; non-null in this builder)

HttpsTransportListener.cs:
 - serverCertificate!.AsX509Certificate2() (CS8602)
 - clientCertificate!.RawData (CS8602; param is nullable but sslPolicyErrors=None guard above)

No runtime behavior change.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

After the master merge of PR #3688 (Certificate manager refactor), GDS
code paths weren't fully aligned with the new ref-counted Certificate
type and CertificateManager API. Fixes by file:

ICertificateGroup.cs: Dictionary<NodeId, Certificate?> (was non-null;
  matches what implementations actually populate).

CertificateGroup.cs: CertificateIssuer property nullable (CS8618 x2);
  fixed dictionary creation X509Certificate2? -> Certificate?;
  telemetry! in OpenStore (provably non-null per surrounding flow).

ApplicationsNodeManager.cs: TrustListManager property nullable (CS8618).

GlobalDiscoverySampleServer.cs: removed obsolete tempIdentity?.Dispose()
  scaffolding (UserIdentity no longer IDisposable post-merge) at lines
  249 and 434 (CS1061 x2); CertificateManager! and userCertificate!
  derefs matching the StandardServer pattern.

GlobalDiscoveryServerClient.cs: localLds declared nullable to allow
  conditional null assignment (CS8600 x2); lds! after ??= with comment.

ServerPushConfigurationClient.cs: m_serverConfiguration! matching
  surrounding pattern.

Tests/.../CertificateStoreTypeTest.cs (2 files): aligned
  LoadPrivateKeyAsync param nullability with ICertificateStore
  signature (CS8767 x4); added ! for nullable trust-list args (CS8604 x2).

No runtime behavior change.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

… merge

After the master merge, Quickstarts.Servers code paths needed nullable
annotations to align with the new Certificate API and master's nullable
property declarations:

MemoryBufferBrowser.cs (lines 140-164):
 - BrowseName.Name typed string?, added ! at use sites
 - m_buffer is nullable in this context, added ! at use sites
 - SizeInBytes is BaseDataVariableState<uint>?, added ! before .Value

ReferenceServer.cs:
 - referenceNodeManager local typed ReferenceNodeManager? (was non-null
   but assigned null on success path; CS8600)
 - Inherited CertificateManager property is nullable; added ! at deref
 - userCertificate parameter is Certificate?; added ! when passing to
   ValidateAsync (the caller path's null check is implicit)

TestDataNodeManager.cs:556:
 - details parameter is ReadRawModifiedDetails?; added ! when passing to
   HistoryDataReader.BeginReadRaw (the path is reached only when details
   is non-null per the method's outer null check)

No runtime behavior change.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>