'NoneType' object is not iterable

Prerequisites

Please answer the following questions for yourself before submitting an issue.

• I am using the latest TensorFlow Model Garden release and TensorFlow 2.
• I am reporting the issue to the correct repository. (Model Garden official or research directory)
• I checked to make sure that this issue has not already been filed.

1. The entire URL of the file you are using

https://github.com/tensorflow/models/tree/master/research/...

2. Describe the bug

When I am doing the evaluation part, I am not able to get the evaluation part they say : for evaluator in evaluators: 'NoneType' object is not iterable

3. Steps to reproduce

Train the model, use the checkpoint for evaluation and see the issue

4. Expected behavior

I am expecting to have the Accuracy for the efficientDet model

5. Additional context

for evaluator in evaluators:
TypeError : 'NoneType' object is not iterable

6. System information

• OS Platform and Distribution (e.g., Linux Ubuntu 16.04):
• Mobile device name if the issue happens on a mobile device:
• TensorFlow installed from (source or binary):
• TensorFlow version (use command below):
• Python version:
• Bazel version (if compiling from source):
• GCC/Compiler version (if compiling from source):
• CUDA/cuDNN version:
• GPU model and memory: