This Flask code raises an error when caching is applied:

This Flask code raises an error when caching is applied:

from flask import Flask
from flask_caching import Cache
app = Flask(__name__)
cache = Cache(app, config={'CACHE_TYPE': 'SimpleCache'})

@app.route('/time')
@cache.cached(timeout=5)
def get_time():
    return time.ctime()

What is the likely cause of the error?