Custom EntityEnderDragon (statue)

Dear Bukkiteers,

I want to create a custom entityenderdragon but I can't really figgure out a good way to let it stay at his current position.

I know I have to override the pathfinding goals.

I have registered the custom entity, and I have this for my entity class:

Code:

import java.lang.reflect.Field;
 
import org.bukkit.craftbukkit.v1_7_R1.util.UnsafeList;
 
import net.minecraft.server.v1_7_R1.EntityEnderDragon;
import net.minecraft.server.v1_7_R1.PathfinderGoalFloat;
import net.minecraft.server.v1_7_R1.PathfinderGoalSelector;
import net.minecraft.server.v1_7_R1.World;
 
public class DragonEntity extends EntityEnderDragon {
 
    public DragonEntity(World world) {
        super(world);
        try {
            Field gsa = PathfinderGoalSelector.class.getDeclaredField("a");
            gsa.setAccessible(true);
            gsa.set(this.goalSelector, new UnsafeList());
            gsa.set(this.targetSelector, new UnsafeList());
        } catch (NoSuchFieldException | SecurityException
                | IllegalArgumentException | IllegalAccessException e) {
            e.printStackTrace();
        }
 
        this.goalSelector.a(0, new PathfinderGoalFloat(this));
    }
}

But this does not work

[19:22:11 WARN]: java.lang.IllegalAccessException: Can not set static final org.
apache.logging.log4j.Logger field net.minecraft.server.v1_7_R1.PathfinderGoalSel
ector.a to org.bukkit.craftbukkit.v1_7_R1.util.UnsafeList

Best Regards,
Maximvdw