Add defaults

src/picture_lister/Picture_Lister.java

@@ -40,6 +40,9 @@ public class Picture_Lister {
             for(int i = 1; i < args.length; i++){
                 file_format[i-1] = args[i];
             }
+        } else {
+            file_format[0] = ".png";
+            file_format[1] = ".jpg";
         }
         System.out.println(picture_dir);
         //Creating a File object for directory