title: can I use conv2d with input dimension not fixed?
body: <p>i am new in tensorflow i have a question : Can i put in my conv2d an input with shape not fixed ?
  inputs.shape =(?, 1568)
  when i train my neural network i get this message :
  <code>raise ValueError(f'Input {input_index} of layer &quot;{layer_name}&quot; ' ValueError: Input 0 of layer &quot;conv2d&quot; is incompatible with the layer: expected min_ndim=4, found ndim=2. Full shape received: (Dimension(None), Dimension(1568))</code>
  my con2d layer is like this :
  <code> x = Conv2D(32, (3,3), padding=&quot;same&quot;,input_shape=input_shape[1:])(inputs)</code></p>