Keras CGRU error message

Using Theano backend.
Traceback (most recent call last):
  File "C:\Users\xxx\AppData\Local\Continuum\Anaconda3\lib\site-packages\theano\tensor\type.py", line 267, in dtype_specs
    }[self.dtype]
KeyError: 'object'

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File "C:\Users\xxx\AppData\Local\Continuum\Anaconda3\lib\site-packages\theano\tensor\basic.py", line 408, in constant_or_value
    TensorType(dtype=x_.dtype, broadcastable=bcastable),
  File "C:\Users\xxx\AppData\Local\Continuum\Anaconda3\lib\site-packages\theano\tensor\type.py", line 50, in __init__
    self.dtype_specs()  # error checking is done there
  File "C:\Users\xxx\AppData\Local\Continuum\Anaconda3\lib\site-packages\theano\tensor\type.py", line 270, in dtype_specs
    % (self.__class__.__name__, self.dtype))
TypeError: Unsupported dtype for TensorType: object

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File "C:\Users\xxx\AppData\Local\Continuum\Anaconda3\lib\site-packages\theano\tensor\basic.py", line 202, in as_tensor_variable
    return constant(x, name=name, ndim=ndim)
  File "C:\Users\xxx\AppData\Local\Continuum\Anaconda3\lib\site-packages\theano\tensor\basic.py", line 422, in constant
    dtype=dtype)
  File "C:\Users\xxx\AppData\Local\Continuum\Anaconda3\lib\site-packages\theano\tensor\basic.py", line 417, in constant_or_value
    raise TypeError("Could not convert %s to TensorType" % x, type(x))
TypeError: ('Could not convert [None] to TensorType', <class 'list'>)

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File "C:/Users/xxx/PycharmProjects/LayerTests/sandbox.py", line 87, in <module>
    updown=up(time_dist)
  File "C:\Users\xxx\AppData\Local\Continuum\Anaconda3\lib\site-packages\keras\engine\topology.py", line 514, in __call__
    self.add_inbound_node(inbound_layers, node_indices, tensor_indices)
  File "C:\Users\xxx\AppData\Local\Continuum\Anaconda3\lib\site-packages\keras\engine\topology.py", line 572, in add_inbound_node
    Node.create_node(self, inbound_layers, node_indices, tensor_indices)
  File "C:\Users\xxx\AppData\Local\Continuum\Anaconda3\lib\site-packages\keras\engine\topology.py", line 149, in create_node
    output_tensors = to_list(outbound_layer.call(input_tensors[0], mask=input_masks[0]))
  File "C:\Users\xxx\AppData\Local\Continuum\Anaconda3\lib\site-packages\keras\layers\recurrent.py", line 215, in call
    input_length=input_shape[1])
  File "C:\Users\xxx\AppData\Local\Continuum\Anaconda3\lib\site-packages\keras\backend\theano_backend.py", line 885, in rnn
    outputs_info=[None] + initial_states,
  File "C:\Users\xxx\AppData\Local\Continuum\Anaconda3\lib\site-packages\theano\tensor\var.py", line 234, in __radd__
    return theano.tensor.basic.add(other, self)
  File "C:\Users\xxx\AppData\Local\Continuum\Anaconda3\lib\site-packages\theano\gof\op.py", line 611, in __call__
    node = self.make_node(*inputs, **kwargs)
  File "C:\Users\xxx\AppData\Local\Continuum\Anaconda3\lib\site-packages\theano\tensor\elemwise.py", line 543, in make_node
    inputs = list(map(as_tensor_variable, inputs))
  File "C:\Users\xxx\AppData\Local\Continuum\Anaconda3\lib\site-packages\theano\tensor\basic.py", line 208, in as_tensor_variable
    raise AsTensorError("Cannot convert %s to TensorType" % str_x, type(x))
theano.tensor.var.AsTensorError: ('Cannot convert [None] to TensorType', <class 'list'>)