Error in running sample_autoencoder.py file

I was following the instructions on the homepage of this github repository, trying to run the sample_autoencoder.py file exactly according to the example. However, this is what showed up:

>python sample_autoencoder.py \
> ../data/best_vae_model.json \
> ../data/best_vae_annealed_weights.h5 \
> ../data/250k_rndm_zinc_drugs_clean.smi \
> ../data/zinc_char_list.json \
> -l5000
Using Theano backend.
Traceback (most recent call last):
File "sample_autoencoder.py", line 97, in
model = model_from_json(json.dumps(model_dict))
File "/usr/local/lib/python2.7/dist-packages/keras/models.py", line 213, in model_from_json
return layer_from_config(config, custom_objects=custom_objects)
File "/usr/local/lib/python2.7/dist-packages/keras/utils/layer_utils.py", line 27, in layer_from_config
class_name = config['class_name']
KeyError: 'class_name'

Can anyone please tell me what is going on here? Thank you very much!