Combining enchants on custom tools 1.15.2

Hi. Currently am working on my mod in 1.15.2, and I noticed that in an anvil I can't combine 2 same type tools together to get the enchants. Example: If I have 1 ruby pickaxe with Unbreaking 3, and another with Fortune 3, I can't combine the 2 picks together to make 1 pick with both enchants, however with Vanilla tools you can do this. Am I missing any code or anything? My Custom tool class just extends PickaxeItem, and I don't really have anything else special in there, just whats required to make it work as a pickaxe. I thought that this would be enough, but clearly I am missing some needed code to make combining enchants on a custom tool available. If anyone could help, I'd greatly appreciate it. I've tried looking at vanilla code, but I don't see anything there, that I don't already have, or don't need. Again, I can enchant the tools, I just can't combine them in an anvil, or with a book either for that matter. Thanks