This application has no explicit mapping for /error, so you are seeing this as a fallback.

package com.teamtreehouse.giflib.controller;

import com.teamtreehouse.giflib.data.GifRepository;
import com.teamtreehouse.giflib.model.Gif;
import jdk.vm.ci.meta.Value;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.stereotype.Controller;
import org.springframework.ui.ModelMap;
import org.springframework.web.bind.annotation.PathVariable;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.ResponseBody;

import java.time.LocalDate;
import java.util.List;

@Controller
public class GifController {
    @Autowired
    private GifRepository gifRepository;

    @RequestMapping(value = "/")
    public String listGifs(ModelMap modelMap) {
        List<Gif> allGifs = gifRepository.getAllGifs();
        modelMap.put("gifs",allGifs);
        return "home";
    }

    @RequestMapping("/gif/{name}")
    public String gifDetails(@PathVariable String name, ModelMap modelMap) {
        Gif gif = gifRepository.findByName(name);
        modelMap.put("gif",gif);
        return "gif-details";
    }

}

package com.teamtreehouse.giflib.data;

import com.teamtreehouse.giflib.model.Gif;
import org.springframework.stereotype.Component;

import java.time.LocalDate;
import java.util.Arrays;
import java.util.List;

@Component
public class GifRepository {
    private static final List<Gif> ALL_GIFS = Arrays.asList(
            new Gif("android-explosion", LocalDate.of(2015,2,13), "Chris Ramacciotti", false),
            new Gif("ben-and-mike", LocalDate.of(2015,10,30), "Ben Jakuben", true),
            new Gif("book-dominos", LocalDate.of(2015,9,15), "Craig Dennis", false),
            new Gif("compiler-bot", LocalDate.of(2015,2,13), "Ada Lovelace", true),
            new Gif("cowboy-coder", LocalDate.of(2015,2,13), "Grace Hopper", false),
            new Gif("infinite-andrew", LocalDate.of(2015,8,23), "Marissa Mayer", true)
    );

    public Gif findByName(String name) {
        for (Gif gif : ALL_GIFS) {
            if(gif.getName().equals(name)) {
                return gif;
            }
        }
        return null;
    }

    public List<Gif> getAllGifs() {
        return ALL_GIFS;
    }

}