input: Write a function named `scrape_webpage` that takes a URL as an input and returns a tuple containing the title and content of the webpage. The function should use the `requests` library to fetch the webpage and the `bs4` (BeautifulSoup) library to parse the HTML and extract the title and content. The title should be extracted using the `title` tag, and the content should be extracted from a `div` element with class 'content'. If the title or content is not found, the function should return `None` for that respective element.
  
  assert scrape_webpage('https://www.example.com')==('Example Domain', 'This domain is for use in illustrative examples in documents. You may use this domain in literature without prior coordination or asking for permission.')
  assert scrape_webpage('https://www.nonexistentwebsite.com')==(None, None)
output: def scrape_webpage(url):
      import requests
      from bs4 import BeautifulSoup
      
      try:
          response = requests.get(url)
          response.raise_for_status()
          soup = BeautifulSoup(response.text, 'html.parser')
          
          title = soup.title.string if soup.title else None
          content_div = soup.find('div', class_='content')
          content = content_div.get_text() if content_div else None
          
          return (title, content)
      except:
          return (None, None)