Add `ToString[]` extension method

StackExchange.Redis/StackExchange/Redis/ExtensionMethods.cs

@@ -111,5 +111,16 @@ public static class ExtensionMethods
             }
             return result;
         }
+
+        static readonly string[] nix = new string[0];
+        /// <summary>
+        /// Create an array of strings from an array of values
+        /// </summary>
+        public static string[] ToStringArray(this RedisValue[] values)
+        {
+            if (values == null) return null;
+            if (values.Length == 0) return nix;
+            return Array.ConvertAll(values, x => (string)x);
+        }
     }
 }