So say I have a button which leads to a new page with an array of photos. If the array has no photos should the button:
Bearing in mind at other times the array will have photos. What is the correct way to handle it?
Usually, and IIRC, services such as one drive, google drive, picasa... will direct you to an empty page, with a clear message stating that the folder/collection/tag/array does not contain any element.
If your application offers it, you would also have a strong emphasis on the action of adding items to this collection, using the easiest method available for your platform (drag n drop, import buttons, take new picture button...)
Doing nothing is the worst thing you can do, because if you have a button, and you can click on it, and sometimes it displays stuff, sometimes it does nothing, it will appear broken.
A warning popup can also be a bad idea in some case, as it suggests either an issue with the application itself, or an error from the user (which you should avoid suggesting as much as possible) that the application cannot gracefully handle.
It is always preferable to help user by preventing mistake(or unexpected or least desired outcome) rather being reactive after least desired outcome. So in the first place where you show the button "go to gallery/array of photos" rename it to something like "add photos". If you still wish to display as "go to gallery" then the yielding page should have a message indicating gallery is empty in a nice tone and an immediate option to make it better that is adding photos right away in the empty page; achieved either through upload, drag drop or any desired means like add from url.
