Fixed NRT warnings.

Author: sdanyliv

Source/LinqToDB.EntityFrameworkCore/LinqToDBExtensionsAdapter.cs

@@ -87,17 +87,21 @@ public Task<TSource> FirstAsync<TSource>(
 			=> EntityFrameworkQueryableExtensions.FirstAsync(source, predicate, token);
 
 		/// <inheritdoc cref="EntityFrameworkQueryableExtensions.FirstOrDefaultAsync{TSource}(IQueryable{TSource}, CancellationToken)"/>
-		public Task<TSource> FirstOrDefaultAsync<TSource>(
+		public Task<TSource?> FirstOrDefaultAsync<TSource>(
 			IQueryable<TSource> source,
 			CancellationToken   token)
+#pragma warning disable CS8619 // Nullability of reference types in value doesn't match target type.
 			=> EntityFrameworkQueryableExtensions.FirstOrDefaultAsync(source, token);
+#pragma warning restore CS8619 // Nullability of reference types in value doesn't match target type.
 
 		/// <inheritdoc cref="EntityFrameworkQueryableExtensions.FirstOrDefaultAsync{TSource}(IQueryable{TSource}, Expression{Func{TSource, bool}}, CancellationToken)"/>
-		public Task<TSource> FirstOrDefaultAsync<TSource>(
+		public Task<TSource?> FirstOrDefaultAsync<TSource>(
 			IQueryable<TSource>            source,
 			Expression<Func<TSource,bool>> predicate,
 			CancellationToken              token)
+#pragma warning disable CS8619 // Nullability of reference types in value doesn't match target type.
 			=> EntityFrameworkQueryableExtensions.FirstOrDefaultAsync(source, predicate, token);
+#pragma warning restore CS8619 // Nullability of reference types in value doesn't match target type.
 
 		/// <inheritdoc cref="EntityFrameworkQueryableExtensions.SingleAsync{TSource}(IQueryable{TSource}, CancellationToken)"/>
 		public Task<TSource> SingleAsync<TSource>(
@@ -113,17 +117,21 @@ public Task<TSource> SingleAsync<TSource>(
 			=> EntityFrameworkQueryableExtensions.SingleAsync(source, predicate, token);
 
 		/// <inheritdoc cref="EntityFrameworkQueryableExtensions.SingleOrDefaultAsync{TSource}(IQueryable{TSource}, CancellationToken)"/>
-		public Task<TSource> SingleOrDefaultAsync<TSource>(
+		public Task<TSource?> SingleOrDefaultAsync<TSource>(
 			IQueryable<TSource> source,
 			CancellationToken   token)
+#pragma warning disable CS8619 // Nullability of reference types in value doesn't match target type.
 			=> EntityFrameworkQueryableExtensions.SingleOrDefaultAsync(source, token);
+#pragma warning restore CS8619 // Nullability of reference types in value doesn't match target type.
 
 		/// <inheritdoc cref="EntityFrameworkQueryableExtensions.SingleOrDefaultAsync{TSource}(IQueryable{TSource}, Expression{Func{TSource, bool}}, CancellationToken)"/>
-		public Task<TSource> SingleOrDefaultAsync<TSource>(
+		public Task<TSource?> SingleOrDefaultAsync<TSource>(
 			IQueryable<TSource>            source,
 			Expression<Func<TSource,bool>> predicate,
 			CancellationToken              token)
+#pragma warning disable CS8619 // Nullability of reference types in value doesn't match target type.
 			=> EntityFrameworkQueryableExtensions.SingleOrDefaultAsync(source, predicate, token);
+#pragma warning restore CS8619 // Nullability of reference types in value doesn't match target type.
 
 		/// <inheritdoc cref="EntityFrameworkQueryableExtensions.ContainsAsync{TSource}(IQueryable{TSource}, TSource, CancellationToken)"/>
 		public Task<bool> ContainsAsync<TSource>(

Source/LinqToDB.EntityFrameworkCore/LinqToDBForEFExtensions.Async.cs

@@ -76,13 +76,13 @@ public static Task<TSource> FirstAsyncLinqToDB<TSource>(
 			=> AsyncExtensions.FirstAsync(source.ToLinqToDB(), predicate, token);
 
 		/// <inheritdoc cref="AsyncExtensions.FirstOrDefaultAsync{TSource}(IQueryable{TSource}, CancellationToken)"/>
-		public static Task<TSource> FirstOrDefaultAsyncLinqToDB<TSource>(
+		public static Task<TSource?> FirstOrDefaultAsyncLinqToDB<TSource>(
 			this IQueryable<TSource> source,
 			CancellationToken        token = default)
 			=> AsyncExtensions.FirstOrDefaultAsync(source.ToLinqToDB(), token);
 
 		/// <inheritdoc cref="AsyncExtensions.FirstOrDefaultAsync{TSource}(IQueryable{TSource}, Expression{Func{TSource, bool}}, CancellationToken)"/>
-		public static Task<TSource> FirstOrDefaultAsyncLinqToDB<TSource>(
+		public static Task<TSource?> FirstOrDefaultAsyncLinqToDB<TSource>(
 			this IQueryable<TSource>       source,
 			Expression<Func<TSource,bool>> predicate,
 			CancellationToken              token = default)
@@ -102,13 +102,13 @@ public static Task<TSource> SingleAsyncLinqToDB<TSource>(
 			=> AsyncExtensions.SingleAsync(source.ToLinqToDB(), predicate, token);
 
 		/// <inheritdoc cref="AsyncExtensions.SingleOrDefaultAsync{TSource}(IQueryable{TSource}, CancellationToken)"/>
-		public static Task<TSource> SingleOrDefaultAsyncLinqToDB<TSource>(
+		public static Task<TSource?> SingleOrDefaultAsyncLinqToDB<TSource>(
 			this IQueryable<TSource> source,
 			CancellationToken        token = default)
 			=> AsyncExtensions.SingleOrDefaultAsync(source.ToLinqToDB(), token);
 
 		/// <inheritdoc cref="AsyncExtensions.SingleOrDefaultAsync{TSource}(IQueryable{TSource}, Expression{Func{TSource, bool}}, CancellationToken)"/>
-		public static Task<TSource> SingleOrDefaultAsyncLinqToDB<TSource>(
+		public static Task<TSource?> SingleOrDefaultAsyncLinqToDB<TSource>(
 			this IQueryable<TSource>       source,
 			Expression<Func<TSource,bool>> predicate,
 			CancellationToken              token = default)

Source/LinqToDB.EntityFrameworkCore/LinqToDBForEFTools.ContextExtensions.cs

@@ -233,6 +233,7 @@ public static async Task<BulkCopyRowsCopied> BulkCopyAsync<T>(
 		[LinqTunnel]
 		[Pure]
 		public static IValueInsertable<T> Into<T>(this DbContext context, ITable<T> target)
+		where T: notnull
 		{
 			if (context == null) throw new ArgumentNullException(nameof(context));
 			if (target == null)  throw new ArgumentNullException(nameof(target));

Source/LinqToDB.EntityFrameworkCore/LinqToDBForEFToolsImplDefault.cs

@@ -331,7 +331,7 @@ protected virtual IDataProvider CreateSqlServerProvider(SqlServerVersion version
 			{
 				providerName = "Microsoft.Data.SqlClient";
 
-				return DataConnection.GetDataProvider(providerName, connectionString)!;
+				return DataConnection.GetDataProvider(providerName, connectionString!)!;
 			}
 
 			switch (version)
@@ -364,7 +364,7 @@ protected virtual IDataProvider CreateSqlServerProvider(SqlServerVersion version
 		protected virtual IDataProvider CreatePostgreSqlProvider(PostgreSQLVersion version, string? connectionString)
 		{
 			if (!string.IsNullOrEmpty(connectionString))
-				return DataConnection.GetDataProvider(ProviderName.PostgreSQL, connectionString)!;
+				return DataConnection.GetDataProvider(ProviderName.PostgreSQL, connectionString!)!;
 
 			string providerName;
 			switch (version)