I have been attempting to make a spear for my mod, and up until now everything had been going fairly well by using the trident as a guide. The problem is that I absolutely cannot get the entity to render. As in, at all. 
I am registering the renderer, and I've confirmed the event is being called for it.
 

@OnlyIn(Dist.CLIENT)
public void ClientSetup(FMLClientSetupEvent event)
{
  if(Config.flailEnabled.get())ModItems.RegisterFlailOverrides();

  MinecraftForge.EVENT_BUS.addListener(ClientEvents::OnClick);
  MinecraftForge.EVENT_BUS.addListener(ClientEvents::OnKeyPressed);

  RenderingRegistry.registerEntityRenderingHandler(ModEntities.SPEAR.get(), RenderSpear::new);
}

The other 3 lines here work perfectly.

Here is the renderer:

public class RenderSpear extends EntityRenderer<SpearEntity>
{
    public RenderSpear(EntityRendererManager manager)
    {
        super(manager);
    }

    @Override
    public void render(SpearEntity spearEntity, float yaw, float partialTicks, MatrixStack matrix, @NotNull IRenderTypeBuffer buffer, int light)
    {
        System.out.println("the funny");
        matrix.pushPose();
        //todo: translate/rotate/scale matrix
        Minecraft mc = Minecraft.getInstance();

        mc.getItemRenderer().render(spearEntity.spearItem, ItemCameraTransforms.TransformType.FIXED, false, matrix, buffer, light, OverlayTexture.NO_OVERLAY, mc.getItemRenderer().getModel(spearEntity.spearItem, spearEntity.level, null));
        matrix.popPose();
    }

    @Override
    public ResourceLocation getTextureLocation(@NotNull SpearEntity entity)
    {
        return null;
    }
}

The println at the top does not print, proving this method is not being called. 

The entity itself works fine, I can throw it and deal damage just like a trident. It just won't render.

For those that might stumble upon this post with the same problem in the future: The solution in this case was to add this to the entity class:

@Override
public IPacket<?> getAddEntityPacket()
{
    return NetworkHooks.getEntitySpawningPacket(this);
}

A rule of thumb: If you custom entity is not a LivingEntity, then you need to override getAddEntityPacket(). This is due to the fact that vanilla handles non-living entity spawn packets in a hard coded way.