FF-1135 - added telegram plugin

Telegram/ExtensionMethods.cs

@@ -0,0 +1,14 @@
+namespace FileFlows.Telegram;
+
+/// <summary>
+/// Extension methods
+/// </summary>
+internal static class ExtensionMethods
+{
+    /// <summary>
+    /// Returns an empty string as null, otherwise returns the original string
+    /// </summary>
+    /// <param name="str">the input string</param>
+    /// <returns>the string or null if empty</returns>
+    public static string? EmptyAsNull(this string str) => str == string.Empty ? null : str;
+}