More logical handling of return values

Ycicle/Program.cs

@@ -51,6 +51,8 @@ namespace Ycicle
                 else
                 {
                     var evaluate = parsed.Evaluate();
+                    if (evaluate == null)
+                        continue;
                     if (parsed.Diagnostics.Messages.Count > 0)
                     {
                         Console.ForegroundColor = ConsoleColor.Red;