Input shape for simple_forecasting

[clu5]

I'm using Python 3 and getting dimension mismatch in keras
Exception: Error when checking model input: expected dense_input_1 to have shape (None, 20) but got array with shape (0, 1)
Can you please tell me what the input should be to the model?

This is my output using model.summary()

____________________________________________________________________________________________________
Layer (type)                     Output Shape          Param #     Connected to                     
====================================================================================================
dense_37 (Dense)                 (None, 500)           10500       dense_input_13[0][0]             
____________________________________________________________________________________________________
activation_30 (Activation)       (None, 500)           0           dense_37[0][0]                   
____________________________________________________________________________________________________
dropout_11 (Dropout)             (None, 500)           0           activation_30[0][0]              
____________________________________________________________________________________________________
dense_38 (Dense)                 (None, 250)           125250      dropout_11[0][0]                 
____________________________________________________________________________________________________
activation_31 (Activation)       (None, 250)           0           dense_38[0][0]                   
____________________________________________________________________________________________________
dense_39 (Dense)                 (None, 1)             251         activation_31[0][0]              
____________________________________________________________________________________________________
activation_32 (Activation)       (None, 1)             0           dense_39[0][0]                   
====================================================================================================
Total params: 136001
____________________________________________________________________________________________________