Initial commit for jackmott#24: [Enhancement] DefaultIfEmptyF should be implemented

- Add Start File

Author: Smurf-IV

LinqFaster/DefaultIfEmpty.cs

@@ -0,0 +1,29 @@
+using System.Runtime.CompilerServices;
+// ReSharper disable ForCanBeConvertedToForeach
+// ReSharper disable UnusedMember.Global
+
+namespace JM.LinqFaster
+{
+    public static partial class LinqFaster
+    {
+        // --------------------------  Arrays --------------------------------------------
+
+        /// <summary>
+        /// Returns an array (For speed) with a single value set to default{T}
+        /// </summary>
+        /// <typeparam name="T"></typeparam>
+        /// <param name="source"></param>
+        /// <returns>source or new array{1}</returns>
+        [MethodImpl(MethodImplOptions.AggressiveInlining)]
+        public static T[] DefaultIfEmptyF<T>(this T[] source)
+        {
+            if ((source == null)
+                || (source.Length == 0)
+                )
+            {
+                return new T[] { default(T) };
+            }
+            return source;
+        }
+    }
+}