MOD ERROR HELP

hello. I am having trouble with trying to make a neck for my hydra boss but in the game it cant spawn and it says:

missing mod: bosses/hydra/hydraneck_Chain at
Terraria.modloader.modloader.gettexture(string name)

I tried to fix it but it still appears. also here is the code:

public override bool PreDraw(Microsoft.Xna.Framework.Graphics.SpriteBatch spriteBatch, Color lightColor)
{
Texture2D texture = ModLoader.GetTexture("bosses/hydra/hydraneck_Chain");...

MOD ERROR HELP