[1.12.2] build error

i have basic class

package ru.sundev.blocks;

import net.minecraft.block.Block;
import net.minecraft.block.material.Material;
import net.minecraft.client.renderer.block.model.ModelResourceLocation;
import net.minecraft.item.Item;
import net.minecraft.item.ItemBlock;
import net.minecraftforge.client.model.ModelLoader;

public class OCCBlock extends Block
{
    public final static String INTERNAL_NAME = "occb_block";

    public OCCBlock()
    {
        super(Material.IRON);
        this.setTranslationKey(INTERNAL_NAME);
        this.setRegistryName(INTERNAL_NAME);
        this.setHardness(2);
        this.setResistance(5);
       // this.setCreativeTab(CreativeTabEnergyConverters.Instance);
    }

    public Item createItemBlock()
    {
        return new ItemBlock(this).setRegistryName(this.getRegistryName());
    }

    public void registerItemModel(Item item)
    {
        ModelLoader.setCustomModelResourceLocation(item, 0, new ModelResourceLocation(this.getRegistryName(), "inventory"));
    }
}

When building i have errors:

Quote

error: cannot access nf
        this.setRegistryName(INTERNAL_NAME);
            ^
  class file for nf not found

Quote

error: cannot access ain
        ModelLoader.setCustomModelResourceLocation(item, 0, new ModelResourceLocation(this.getRegistryName(), "inventory"));
                   ^
  class file for ain not found

Quote

error: cannot access avj
        GameRegistry.registerTileEntity(TileEntityOCCBlock.class, new ResourceLocation(occb.MOD_ID, "tileentity_occb"));
                    ^
  class file for avj not found

what is "nf", "ain", "avj"? and how to fix this. ty

btw. iam using intellij idea