[1.11] Can't use ItemStack.EMPTY?

[thefinaluptake]

For some reason, my mod cannot use ItemStack.EMPTY. I look at the source codes for many other mods, and they use it just fine. I have to instead use ItemStack.field_190927_a. At least, I think that works, I'm not sure since there's other things in my code that also are not working even though they should be(for example, I can't override onBlockActivated for some strange reason). I'm using Idea, and I followed cpw's video on installing Forge through Idea. I wish I could give you a bit more details, but I've got no clue what the issue is. I'm using the latest version of forge, and I've tried reinstalling gradle and all that many times.

[shadowfacts]

In your build.gradle file, you should change the mappings version to the latest. MCP mappings snapshots are published daily with the form of snapshot_YYYYMMDD, so today's would be snapshot_20161202.

[thefinaluptake]

Thanks! Sorry if this was an obvious thing, this is my first time ever touching modding.