Problem with param.grad in custom defined Module

When I build a custom Module, performing updates doesn’t work as param.grad is not defined. I’m not exactly sure what’s wrong.

The class is defined as such,

class vanillaLargeRNN(nn.Module):
    def __init__(self, input_shape, hidden_shape, output_shape):
        super(vanillaLargeRNN, self).__init__()

        self.hidden_shape = hidden_shape
        self.input2hidden = nn.Linear(input_shape + hidden_shape, hidden_shape)
        self.input2output = nn.Linear(input_shape + hidden_shape, output_shape)
        self.output2output = nn.Linear(output_shape + hidden_shape, output_shape)
        self.input2hidden2 = nn.Linear(input_shape + hidden_shape, hidden_shape)
        self.input2output2 = nn.Linear(input_shape + hidden_shape, output_shape)
        self.output2output2 = nn.Linear(output_shape + hidden_shape, output_shape)
        self.input2hidden3 = nn.Linear(input_shape + hidden_shape, hidden_shape)
        self.input2output3 = nn.Linear(input_shape + hidden_shape, output_shape)
        self.output2output3 = nn.Linear(output_shape + hidden_shape, output_shape)
        self.dropout1 = nn.Dropout(0.3)
        self.dropout2 = nn.Dropout(0.3)
        self.dropout3 = nn.Dropout(0.3)

    def forward(self, input, hidden1, hidden2, hidden3):
        input_comb =[input, hidden1], 1)
        hidden = self.input2hidden(input_comb)
        output_temp = self.input2output(input_comb)
        output_comb =[output_temp, hidden1], 1)
        output = self.output2output(output_comb)
        output = self.dropout1(output)
        input_comb2 =[output, hidden2], 1)
        hidden2 = self.input2hidden2(input_comb2)
        output_temp2 = self.input2output2(input_comb2)
        output_comb2 =[output_temp2, hidden2], 1)
        output2 = self.output2output2(output_comb2)
        output2 = self.dropout2(output2)
        input_comb3 =[output2, hidden3], 1)
        hidden3 = self.input2hidden3(input_comb3)
        output_temp3 = self.input2output3(input_comb3)
        output_comb3 =[output_temp3, hidden3], 1)
        output3 = self.output2output3(output_comb3)
        output3 = self.dropout3(output3)        
        return output3, hidden1, hidden2, hidden3

And I am performing updates as such,

for i in range(min(input_line_vec.size()[0], 150)):
        output, hidden1, hidden2, hidden3 = rnn.forward(input_line_vec[i], hidden1, hidden2, hidden3)
        loss += criterion(output, target_line_vec[i])

    for param in rnn.parameters():,

this makes no sense. param.grad will and has to be defined. Is there a minimal script i can run locally to reproduce this?