UnimplementedError: TensorArray has size zero, but element shape <unknown> is not fully defined. Currently only static shapes are supported when packing zero-size TensorArrays about sequence_tagging

[guillaumegenthial]

Hi @MingjieQian,
Hard to tell what problem it is. Probably have to do with your TF install. It seems like there were some issues for sentences of length 1 with the CRF but it seems like your error is different.
I tested on my laptop with a sentence of length 1 and a word of length 1 and it seems to work.
In case that might help, here is a snapshot of my environment:
backports.weakref==1.0.post1 bleach==1.5.0 click==6.7 enum34==1.1.6 Flask==0.12.2 Flask-Cors==3.0.3 funcsigs==1.0.2 futures==3.2.0 gunicorn==19.7.1 html5lib==0.9999999 itsdangerous==0.24 Jinja2==2.10 Markdown==2.6.10 MarkupSafe==1.0 mock==2.0.0 numpy==1.13.3 pbr==3.1.1 protobuf==3.5.1 scipy==1.0.0 six==1.11.0 tensorflow==1.4.1 tensorflow-tensorboard==0.4.0rc3 Werkzeug==0.14.1

Try using a virtual env with a cpu version of tensorflow!

[MingjieQian]

Thanks very much for your help, Guilla. A cpu version of TF works.