Expected a symbolic tensor instance?

alueError: Unexpectedly found an instance of type <class 'numpy.ndarray'>. Expected a symbolic tensor instance.
That’s the error message from Keras Backend I get when I try to predict. I am using a CTCloss function from this example https://github.com/ysoullard/CTCModel/blob/master/CTCModel.py the test set is a numpy array [features_test, input_lengths_test]. I tried converting it to a tensor but didn’t convert