title: Autoencoder MaxUnpool2d missing 'Indices' argument
body: <p>The following model returns the error: 
  <strong>TypeError: forward() missing 1 required positional argument: 'indices'</strong></p>
  
  <p>I've exhausted many online examples and they all look similar to my code. My maxpool layer returns both the input and the indices for the unpool layer. Any ideas on what's wrong?</p>
  
  <pre><code>class autoencoder(nn.Module):
  def __init__(self):
      super(autoencoder, self).__init__()
      self.encoder = nn.Sequential(
          ...
          nn.MaxPool2d(2, stride=1, return_indices=True)
      )
      self.decoder = nn.Sequential(
          nn.MaxUnpool2d(2, stride=1),
          ...
      )
  
  def forward(self, x):
      x = self.encoder(x)
      x = self.decoder(x)
      return x
  </code></pre>