Guard newer APIs to preserve netstandard2.0 compatibility

SharedCode.Core/Data/DataReaderExtensions.cs

@@ -80,7 +80,11 @@ public static IList<string> ToDelimited(this IDataReader @this, string separator
 					if (@this.GetFieldType(index) == typeof(string))
 					{
 						// If double quotes are used in value, ensure each are replaced but 2.
-						if (value?.Contains('"', StringComparison.Ordinal) == true)
+#if NETSTANDARD2_1_OR_GREATER || NET6_0_OR_GREATER
+						if (value?.IndexOf('"', StringComparison.Ordinal) >= 0)
+#else
+						if (value?.IndexOf('"') >= 0)
+#endif
 						{
 #if NETSTANDARD2_1_OR_GREATER || NET6_0_OR_GREATER
 							value = value.Replace("\"", "\"\"", StringComparison.Ordinal);
@@ -89,8 +93,8 @@ public static IList<string> ToDelimited(this IDataReader @this, string separator
 #endif
 						}
 
-						// If separtor are is in value, ensure it is put in double quotes.
-						if (value?.Contains(separator, StringComparison.Ordinal) == true)
+						// If separator is in value, ensure it is put in double quotes.
+						if (value?.IndexOf(separator, StringComparison.Ordinal) >= 0)
 						{
 							value = $"\"{value}\"";
 						}

SharedCode.Core/IO/BufferedWriter.cs

@@ -67,7 +67,13 @@ public async Task FullFlushAsync(CancellationToken token)
 
 		if (this.StringBuilder.Length > 0)
 		{
+#if NET8_0_OR_GREATER
 			await this.writer.WriteAsync(this.StringBuilder, token).ConfigureAwait(false);
+#else
+			token.ThrowIfCancellationRequested();
+			// Older targets do not expose a cancellable TextWriter string overload.
+			await this.writer.WriteAsync(this.StringBuilder.ToString()).ConfigureAwait(false);
+#endif
 			_ = this.StringBuilder.Clear();
 		}
 
@@ -102,7 +108,13 @@ public async Task StrongFlushAsync(CancellationToken token)
 
 		if (this.StringBuilder.Length > 0)
 		{
+#if NET8_0_OR_GREATER
 			await this.writer.WriteAsync(this.StringBuilder, token).ConfigureAwait(true);
+#else
+			token.ThrowIfCancellationRequested();
+			// Older targets do not expose a cancellable TextWriter string overload.
+			await this.writer.WriteAsync(this.StringBuilder.ToString()).ConfigureAwait(true);
+#endif
 			_ = this.StringBuilder.Clear();
 		}
 	}
@@ -128,7 +140,13 @@ public async Task WeakFlushAsync(CancellationToken token = default)
 	{
 		if (this.StringBuilder.Length > BufferLength)
 		{
+#if NET8_0_OR_GREATER
 			await this.writer.WriteAsync(this.StringBuilder, token).ConfigureAwait(true);
+#else
+			token.ThrowIfCancellationRequested();
+			// Older targets do not expose a cancellable TextWriter string overload.
+			await this.writer.WriteAsync(this.StringBuilder.ToString()).ConfigureAwait(true);
+#endif
 			_ = this.StringBuilder.Clear();
 		}
 	}

SharedCode.Core/Linq/EnumerableExtensions.cs

@@ -271,8 +271,19 @@ public static int IndexOf<TSource>(this IEnumerable<TSource> @this, TSource valu
 	/// <returns>
 	/// <c>true</c> if the source enumerable is not null and contains items; otherwise, <c>false</c>.
 	/// </returns>
-	public static bool IsNotNullOrEmpty<T>(this IEnumerable<T> @this) =>
-		@this is not null && (@this.TryGetNonEnumeratedCount(out var count) ? count > 0 : @this.Any());
+	public static bool IsNotNullOrEmpty<T>(this IEnumerable<T> @this)
+	{
+		if (@this is null)
+		{
+			return false;
+		}
+
+#if NET6_0_OR_GREATER
+		return @this.TryGetNonEnumeratedCount(out var count) ? count > 0 : @this.Any();
+#else
+		return @this.Any();
+#endif
+	}
 
 	/// <summary>
 	/// Determines whether the source enumerable is null or contains no items.