.Net: Fix nullable reference type warnings (#3510)

### Motivation and Context

I temporarily retargeted all of the projects to net8.0 and fixed all of
the NRT warnings, some of which were noise, and some of which were
legit.

### Contribution Checklist

<!-- Before submitting this PR, please make sure: -->

- [x] The code builds clean without any errors or warnings
- [x] The PR follows the [SK Contribution
Guidelines](https://github.com/microsoft/semantic-kernel/blob/main/CONTRIBUTING.md)
and the [pre-submission formatting
script](https://github.com/microsoft/semantic-kernel/blob/main/CONTRIBUTING.md#development-scripts)
raises no violations
- [x] All unit tests pass, and I have added new tests where possible
- [x] I didn't break anyone 😄

---------

Co-authored-by: Roger Barreto <19890735+RogerBarreto@users.noreply.github.com>

dotnet/src/Connectors/Connectors.AI.HuggingFace/TextEmbedding/HuggingFaceTextEmbeddingGeneration.cs

@@ -70,17 +70,16 @@ public HuggingFaceTextEmbeddingGeneration(string model, HttpClient httpClient, s
     {
         Verify.NotNullOrWhiteSpace(model);
         Verify.NotNull(httpClient);
-
-        this._model = model;
-        this._endpoint = endpoint;
-        this._httpClient = httpClient;
-        this._attributes.Add(IAIServiceExtensions.ModelIdKey, this._model);
-        this._attributes.Add(IAIServiceExtensions.EndpointKey, this._endpoint ?? this._httpClient.BaseAddress.ToString());
-
         if (httpClient.BaseAddress == null && string.IsNullOrEmpty(endpoint))
         {
             throw new SKException("The HttpClient BaseAddress and endpoint are both null or empty. Please ensure at least one is provided.");
         }
+
+        this._model = model;
+        this._endpoint = endpoint;
+        this._httpClient = httpClient;
+        this._attributes.Add(IAIServiceExtensions.ModelIdKey, model);
+        this._attributes.Add(IAIServiceExtensions.EndpointKey, endpoint ?? httpClient.BaseAddress!.ToString());
     }
 
     /// <inheritdoc/>

dotnet/src/Connectors/Connectors.AI.OpenAI/AzureSdk/ClientBase.cs

@@ -61,7 +61,7 @@ private protected ClientBase(ILoggerFactory? loggerFactory = null)
     /// <summary>
     /// Instance of <see cref="Meter"/> for metrics.
     /// </summary>
-    private static readonly Meter s_meter = new(typeof(ClientBase).Assembly.GetName().Name);
+    private static readonly Meter s_meter = new(typeof(ClientBase).Assembly.GetName().Name!);
 
     /// <summary>
     /// Instance of <see cref="Counter{T}"/> to keep track of the number of prompt tokens used.

dotnet/src/Connectors/Connectors.AI.OpenAI/ChatCompletionWithData/ChatWithDataResult.cs

@@ -34,7 +34,9 @@ public Task<ChatMessageBase> GetChatMessageAsync(CancellationToken cancellationT
         var message = this._choice.Messages
             .FirstOrDefault(message => message.Role.Equals(AuthorRole.Assistant.Label, StringComparison.Ordinal));
 
-        return Task.FromResult<ChatMessageBase>(new SKChatMessage(message.Role, message.Content));
+        return message is not null ?
+            Task.FromResult<ChatMessageBase>(new SKChatMessage(message.Role, message.Content)) :
+            Task.FromException<ChatMessageBase>(new SKException("No message found"));
     }
 
     public async Task<string> GetCompletionAsync(CancellationToken cancellationToken = default)

dotnet/src/Connectors/Connectors.Memory.AzureCognitiveSearch/AzureCognitiveSearchMemoryStore.cs

@@ -399,7 +399,7 @@ private string NormalizeIndexName(string indexName)
     private SearchClient GetSearchClient(string indexName)
     {
         // Search an available client from the local cache
-        if (!this._clientsByIndex.TryGetValue(indexName, out SearchClient client))
+        if (!this._clientsByIndex.TryGetValue(indexName, out SearchClient? client))
         {
             client = this._adminClient.GetSearchClient(indexName);
             this._clientsByIndex[indexName] = client;

dotnet/src/Connectors/Connectors.Memory.Chroma/ChromaClient.cs

@@ -31,6 +31,8 @@ public class ChromaClient : IChromaClient
     /// <param name="loggerFactory">The <see cref="ILoggerFactory"/> to use for logging. If null, no logging will be performed.</param>
     public ChromaClient(string endpoint, ILoggerFactory? loggerFactory = null)
     {
+        Verify.NotNull(endpoint);
+
         this._httpClient = new HttpClient(NonDisposableHttpClientHandler.Instance, disposeHandler: false);
         this._endpoint = endpoint;
         this._logger = loggerFactory is not null ? loggerFactory.CreateLogger(typeof(ChromaClient)) : NullLogger.Instance;
@@ -166,10 +168,10 @@ public async Task<ChromaQueryResultModel> QueryEmbeddingsAsync(string collection
         HttpRequestMessage request,
         CancellationToken cancellationToken = default)
     {
-        string endpoint = this._endpoint ?? this._httpClient.BaseAddress.ToString();
+        string endpoint = this._endpoint ?? this._httpClient.BaseAddress!.ToString();
         endpoint = this.SanitizeEndpoint(endpoint);
 
-        string operationName = request.RequestUri.ToString();
+        string operationName = request.RequestUri!.ToString();
 
         request.RequestUri = new Uri(new Uri(endpoint), operationName);
 

dotnet/src/Connectors/Connectors.Memory.Pinecone/Model/PodType.cs

@@ -108,7 +108,7 @@ public override PodType Read(ref Utf8JsonReader reader, Type typeToConvert, Json
         object? enumValue = Enum
             .GetValues(typeToConvert)
             .Cast<object?>()
-            .FirstOrDefault(value => value != null && typeToConvert.GetMember(value.ToString())[0]
+            .FirstOrDefault(value => value != null && typeToConvert.GetMember(value.ToString()!)[0]
                 .GetCustomAttribute(typeof(EnumMemberAttribute)) is EnumMemberAttribute enumMemberAttr && enumMemberAttr.Value == stringValue);
 
         if (enumValue != null)

dotnet/src/Connectors/Connectors.Memory.Pinecone/PineconeClient.cs

@@ -551,7 +551,7 @@ private string GetIndexOperationsApiBasePath()
 
     private async Task<string> GetIndexHostAsync(string indexName, CancellationToken cancellationToken = default)
     {
-        if (this._indexHostMapping.TryGetValue(indexName, out string indexHost))
+        if (this._indexHostMapping.TryGetValue(indexName, out string? indexHost))
         {
             return indexHost;
         }

dotnet/src/Connectors/Connectors.Memory.Pinecone/PineconeUtils.cs

@@ -86,7 +86,7 @@ await foreach (PineconeDocument document in documents)
                 continue;
             }
 
-            if (!document.Metadata.TryGetValue("text", out object value))
+            if (!document.Metadata.TryGetValue("text", out object? value))
             {
                 yield return document;
 
@@ -159,7 +159,7 @@ await foreach (PineconeDocument record in data)
             currentBatch = new List<PineconeDocument>(batchSize);
         }
 
-        if (currentBatch.Count <= 0)
+        if (currentBatch.Count == 0)
         {
             yield break;
         }
@@ -177,13 +177,6 @@ private static int GetMetadataSize(Dictionary<string, object> metadata)
         return (int)stream.Length;
     }
 
-    private static int GetEntrySize(KeyValuePair<string, object> entry)
-    {
-        Dictionary<string, object> temp = new() { { entry.Key, entry.Value } };
-
-        return GetMetadataSize(temp);
-    }
-
     /// <summary>
     ///  Utility method to convert a dictionary of filters to the format expected by Pinecone.
     /// </summary>

dotnet/src/Connectors/Connectors.Memory.Qdrant/Diagnostics/Verify.cs

@@ -81,8 +81,7 @@ static bool IsReservedIpAddress(string host)
             throw new ArgumentException($"The {name} `{url}` is incomplete, enter a valid URL starting with 'https://", name);
         }
 
-        bool result = Uri.TryCreate(url, UriKind.Absolute, out var uri);
-        if (!result || string.IsNullOrEmpty(uri.Host))
+        if (!Uri.TryCreate(url, UriKind.Absolute, out var uri) || string.IsNullOrEmpty(uri.Host))
         {
             throw new ArgumentException($"The {name} `{url}` is not valid", name);
         }

dotnet/src/Connectors/Connectors.Memory.Qdrant/QdrantVectorDbClient.cs

@@ -480,7 +480,7 @@ private static Uri SanitizeEndpoint(string endpoint, int? port = null)
         //Apply endpoint override if it's specified.
         if (this._endpointOverride != null)
         {
-            request.RequestUri = new Uri(this._endpointOverride, request.RequestUri);
+            request.RequestUri = new Uri(this._endpointOverride, request.RequestUri!);
         }
 
         HttpResponseMessage response = await this._httpClient.SendWithSuccessCheckAsync(request, cancellationToken).ConfigureAwait(false);

dotnet/src/Connectors/Connectors.Memory.Weaviate/WeaviateMemoryStore.cs

@@ -321,12 +321,12 @@ public async Task<string> UpsertAsync(string collectionName, MemoryRecord record
 
         DateTimeOffset? timestamp = weaviateObject.Properties == null
             ? null
-            : weaviateObject.Properties.TryGetValue("sk_timestamp", out object value)
+            : weaviateObject.Properties.TryGetValue("sk_timestamp", out object? value)
                 ? Convert.ToDateTime(value.ToString(), CultureInfo.InvariantCulture)
                 : null;
 
         MemoryRecord record = new(
-            key: weaviateObject.Id!,
+            key: weaviateObject.Id,
             timestamp: timestamp,
             embedding: weaviateObject.Vector,
             metadata: ToMetadata(weaviateObject));
@@ -502,7 +502,7 @@ private static MemoryRecord DeserializeToMemoryRecord(JsonNode? json)
     // Get a class description, useful for checking name collisions
     private static string ToWeaviateFriendlyClassDescription(string collectionName)
     {
-        return $"{"Semantic Kernel memory store for collection:"} {collectionName}";
+        return $"Semantic Kernel memory store for collection: {collectionName}";
     }
 
     // Convert a collectionName to a valid Weaviate class name
@@ -528,7 +528,7 @@ private static string ToWeaviateFriendlyClassName(string collectionName)
         var apiVersion = !string.IsNullOrWhiteSpace(this._apiVersion) ? this._apiVersion : DefaultApiVersion;
         var baseAddress = this._endpoint ?? this._httpClient.BaseAddress;
 
-        request.RequestUri = new Uri(baseAddress, $"{apiVersion}/{request.RequestUri}");
+        request.RequestUri = new Uri(baseAddress!, $"{apiVersion}/{request.RequestUri}");
 
         if (!string.IsNullOrEmpty(this._apiKey))
         {
@@ -564,10 +564,10 @@ private static MemoryRecordMetadata ToMetadata(WeaviateObject weaviateObject)
         return new(
             false,
             string.Empty,
-            weaviateObject.Properties["sk_id"].ToString(),
-            weaviateObject.Properties["sk_description"].ToString(),
-            weaviateObject.Properties["sk_text"].ToString(),
-            weaviateObject.Properties["sk_additional_metadata"].ToString()
+            weaviateObject.Properties["sk_id"].ToString() ?? string.Empty,
+            weaviateObject.Properties["sk_description"].ToString() ?? string.Empty,
+            weaviateObject.Properties["sk_text"].ToString() ?? string.Empty,
+            weaviateObject.Properties["sk_additional_metadata"].ToString() ?? string.Empty
         );
     }
 }

dotnet/src/Functions/Functions.Grpc/GrpcOperationRunner.cs

@@ -219,12 +219,12 @@ private static TypeInfo BuildGrpcOperationDataContractType(GrpcOperationDataCont
             propertyBuilder.SetSetMethod(setterBuilder);
 
             //Add ProtoMember attribute to the data contract with tag/number
-            var dataMemberAttributeBuilder = new CustomAttributeBuilder(typeof(ProtoMemberAttribute).GetConstructor(new[] { typeof(int) }), new object[] { field.Number });
+            var dataMemberAttributeBuilder = new CustomAttributeBuilder(typeof(ProtoMemberAttribute).GetConstructor(new[] { typeof(int) })!, new object[] { field.Number });
             propertyBuilder.SetCustomAttribute(dataMemberAttributeBuilder);
         }
 
         //Add ProtoContract attribute to the data contract
-        var dataContractAttributeBuilder = new CustomAttributeBuilder(typeof(ProtoContractAttribute).GetConstructor(Type.EmptyTypes), Array.Empty<object>());
+        var dataContractAttributeBuilder = new CustomAttributeBuilder(typeof(ProtoContractAttribute).GetConstructor(Type.EmptyTypes)!, Array.Empty<object>());
         typeBuilder.SetCustomAttribute(dataContractAttributeBuilder);
 
         var type = typeBuilder.CreateTypeInfo();

dotnet/src/Functions/Functions.Grpc/Protobuf/ProtoDocumentParser.cs

@@ -126,15 +126,16 @@ private List<GrpcOperationDataContractTypeFiled> GetDataContractFields(List<Fiel
     private static string GetProtobufDataTypeName(FieldDescriptorProto.Type type)
     {
         var fieldInfo = typeof(FieldDescriptorProto.Type).GetField(type.ToString());
-
-        //Get protobuf type name from enum attribute - [global::ProtoBuf.ProtoEnum(Name = @"TYPE_DOUBLE")]
-        var attribute = (ProtoEnumAttribute)Attribute.GetCustomAttribute(fieldInfo, typeof(ProtoEnumAttribute));
-
-        if (attribute == null)
+        if (fieldInfo != null)
         {
-            throw new SKException($"Impossible to find protobuf type name corresponding to '{type}' type.");
+            //Get protobuf type name from enum attribute - [global::ProtoBuf.ProtoEnum(Name = @"TYPE_DOUBLE")]
+            var attribute = (ProtoEnumAttribute?)Attribute.GetCustomAttribute(fieldInfo, typeof(ProtoEnumAttribute));
+            if (attribute != null)
+            {
+                return attribute.Name;
+            }
         }
 
-        return attribute.Name;
+        throw new SKException($"Impossible to find protobuf type name corresponding to '{type}' type.");
     }
 }

dotnet/src/Functions/Functions.OpenAPI/Builders/Serialization/ArrayParameterValueSerializer.cs

@@ -38,7 +38,7 @@ public static string SerializeArrayAsSeparateParameters(string name, JsonArray a
     /// <returns>A string containing the serialized parameter.</returns>
     public static string SerializeArrayAsDelimitedValues(JsonArray array, string delimiter)
     {
-        var values = new List<string>();
+        var values = new List<string?>();
 
         foreach (var item in array)
         {

dotnet/src/Functions/Functions.OpenAPI/Model/RestApiOperationResponseConverter.cs

@@ -12,13 +12,13 @@ namespace Microsoft.SemanticKernel.Functions.OpenAPI.Model;
 public class RestApiOperationResponseConverter : TypeConverter
 {
     /// <inheritdoc/>
-    public override bool CanConvertTo(ITypeDescriptorContext context, Type destinationType)
+    public override bool CanConvertTo(ITypeDescriptorContext? context, Type? destinationType)
     {
         return destinationType == typeof(string) || base.CanConvertTo(context, destinationType);
     }
 
     /// <inheritdoc/>
-    public override object ConvertTo(ITypeDescriptorContext context, CultureInfo culture, object value, Type destinationType)
+    public override object? ConvertTo(ITypeDescriptorContext? context, CultureInfo? culture, object? value, Type destinationType)
     {
         // Convert object content to a string based on the type of the `Content` property.
         // More granular conversion logic can be built based on the value of the `ContentType` property, if needed.

dotnet/src/Functions/Functions.OpenAPI/OpenApi/OpenApiDocumentParser.cs

@@ -231,8 +231,8 @@ private static List<RestApiOperationParameter> CreateRestApiOperationParameters(
                 parameter.Schema.Type,
                 parameter.Required,
                 parameter.Explode,
-                (RestApiOperationParameterLocation)Enum.Parse(typeof(RestApiOperationParameterLocation), parameter.In.ToString()),
-                (RestApiOperationParameterStyle)Enum.Parse(typeof(RestApiOperationParameterStyle), parameter.Style.ToString()),
+                (RestApiOperationParameterLocation)Enum.Parse(typeof(RestApiOperationParameterLocation), parameter.In.ToString()!),
+                (RestApiOperationParameterStyle)Enum.Parse(typeof(RestApiOperationParameterStyle), parameter.Style.ToString()!),
                 parameter.Schema.Items?.Type,
                 GetParameterValue(parameter.Name, parameter.Schema.Default),
                 parameter.Description,

dotnet/src/Functions/Functions.OpenAPI/RestApiOperationRunner.cs

@@ -183,7 +183,11 @@ private static async Task<RestApiOperationResponse> SerializeResponseContentAsyn
     {
         var contentType = content.Headers.ContentType;
 
-        var mediaType = contentType.MediaType;
+        var mediaType = contentType?.MediaType;
+        if (mediaType is null)
+        {
+            throw new SKException("No media type available.");
+        }
 
         // Obtain the content serializer by media type (e.g., text/plain, application/json, image/jpg)  
         if (!s_serializerByContentType.TryGetValue(mediaType, out var serializer))
@@ -207,7 +211,7 @@ private static async Task<RestApiOperationResponse> SerializeResponseContentAsyn
         // Serialize response content and return it  
         var serializedContent = await serializer.Invoke(content).ConfigureAwait(false);
 
-        return new RestApiOperationResponse(serializedContent, contentType.ToString());
+        return new RestApiOperationResponse(serializedContent, contentType!.ToString());
     }
 
     /// <summary>

dotnet/src/Planners/Planners.Core/Action/ActionPlanner.cs

@@ -134,9 +134,9 @@ public async Task<Plan> CreatePlanAsync(string goal, CancellationToken cancellat
         {
             foreach (KeyValuePair<string, object> p in planData.Plan.Parameters)
             {
-                if (p.Value != null)
+                if (p.Value?.ToString() is string value)
                 {
-                    plan.Steps[0].Parameters[p.Key] = p.Value.ToString();
+                    plan.Steps[0].Parameters[p.Key] = value;
                 }
             }
         }
@@ -263,24 +263,25 @@ No parameters.
     /// <returns>Instance of <see cref="ActionPlanResponse"/> object deserialized from extracted JSON.</returns>
     private ActionPlanResponse? ParsePlannerResult(FunctionResult plannerResult)
     {
-        Match match = s_planRegex.Match(plannerResult.GetValue<string>());
-
-        if (match.Success && match.Groups["Close"].Length > 0)
+        if (plannerResult.GetValue<string>() is string result)
         {
-            string planJson = $"{{{match.Groups["Close"]}}}";
-            try
-            {
-                return JsonSerializer.Deserialize<ActionPlanResponse?>(planJson, s_actionPlayResponseOptions);
-            }
-            catch (Exception e)
+            Match match = s_planRegex.Match(result);
+
+            if (match.Success && match.Groups["Close"] is { Length: > 0 } close)
             {
-                throw new SKException("Plan parsing error, invalid JSON", e);
+                string planJson = $"{{{close}}}";
+                try
+                {
+                    return JsonSerializer.Deserialize<ActionPlanResponse?>(planJson, s_actionPlayResponseOptions);
+                }
+                catch (Exception e)
+                {
+                    throw new SKException("Plan parsing error, invalid JSON", e);
+                }
             }
         }
-        else
-        {
-            throw new SKException($"Failed to extract valid json string from planner result: '{plannerResult}'");
-        }
+
+        throw new SKException($"Failed to extract valid json string from planner result: '{plannerResult}'");
     }
 
     private void PopulateList(StringBuilder list, IEnumerable<FunctionView> functions)

dotnet/src/Planners/Planners.Core/Action/InstrumentedActionPlanner.cs

@@ -87,12 +87,12 @@ public async Task<Plan> CreatePlanAsync(string goal, CancellationToken cancellat
     /// <summary>
     /// Instance of <see cref="ActivitySource"/> for planner-related activities.
     /// </summary>
-    private static readonly ActivitySource s_activitySource = new(typeof(InstrumentedActionPlanner).FullName);
+    private static readonly ActivitySource s_activitySource = new(typeof(InstrumentedActionPlanner).FullName!);
 
     /// <summary>
     /// Instance of <see cref="Meter"/> for planner-related metrics.
     /// </summary>
-    private static readonly Meter s_meter = new(typeof(InstrumentedActionPlanner).FullName);
+    private static readonly Meter s_meter = new(typeof(InstrumentedActionPlanner).FullName!);
 
     /// <summary>
     /// Instance of <see cref="Histogram{T}"/> to record plan creation execution time.

dotnet/src/Planners/Planners.Core/Sequential/InstrumentedSequentialPlanner.cs

@@ -87,12 +87,12 @@ public async Task<Plan> CreatePlanAsync(string goal, CancellationToken cancellat
     /// <summary>
     /// Instance of <see cref="ActivitySource"/> for planner-related activities.
     /// </summary>
-    private static readonly ActivitySource s_activitySource = new(typeof(InstrumentedSequentialPlanner).FullName);
+    private static readonly ActivitySource s_activitySource = new(typeof(InstrumentedSequentialPlanner).FullName!);
 
     /// <summary>
     /// Instance of <see cref="Meter"/> for planner-related metrics.
     /// </summary>
-    private static readonly Meter s_meter = new(typeof(InstrumentedSequentialPlanner).FullName);
+    private static readonly Meter s_meter = new(typeof(InstrumentedSequentialPlanner).FullName!);
 
     /// <summary>
     /// Instance of <see cref="Histogram{T}"/> to record plan creation execution time.

dotnet/src/Planners/Planners.Core/Stepwise/InstrumentedStepwisePlanner.cs

@@ -80,12 +80,12 @@ public Plan CreatePlan(string goal)
     /// <summary>
     /// Instance of <see cref="ActivitySource"/> for planner-related activities.
     /// </summary>
-    private static readonly ActivitySource s_activitySource = new(typeof(InstrumentedStepwisePlanner).FullName);
+    private static readonly ActivitySource s_activitySource = new(typeof(InstrumentedStepwisePlanner).FullName!);
 
     /// <summary>
     /// Instance of <see cref="Meter"/> for planner-related metrics.
     /// </summary>
-    private static readonly Meter s_meter = new(typeof(InstrumentedStepwisePlanner).FullName);
+    private static readonly Meter s_meter = new(typeof(InstrumentedStepwisePlanner).FullName!);
 
     /// <summary>
     /// Instance of <see cref="Histogram{T}"/> to record plan creation execution time.