Error in object detection using ssd_mobilenet_v1_ppn_

System information

• Have I written custom code (as opposed to using a stock example script provided in TensorFlow): No
• OS Platform and Distribution (e.g., Linux Ubuntu 16.04): Win10
• Mobile device (e.g., Pixel 4, Samsung Galaxy 10) if the issue happens on mobile device: no
• TensorFlow installed from (source or binary): binary
• TensorFlow version (use command below): 1.15.0
• Python version: 3.7
• Bazel version (if compiling from source): na
• GCC/Compiler version (if compiling from source): na
• CUDA/cuDNN version: 10.0 / 7.6
• GPU model and memory:

When i train per detection using pretrained model here:
ssd_mobilenet_v1_ppn_shared_box_predictor_300x300_coco14_sync_2018_07_03

I have follow error:
Traceback (most recent call last):
File "object_detection/model_main.py", line 109, in
tf.app.run()
File "C:\Users\enrico.beltramo.conda\envs\objdecbase\lib\site-packages\tensorflow_core\python\platform\app.py", line 40, in run
_run(main=main, argv=argv, flags_parser=_parse_flags_tolerate_undef)
File "C:\Users\enrico.beltramo.conda\envs\objdecbase\lib\site-packages\absl\app.py", line 299, in run
_run_main(main, args)
File "C:\Users\enrico.beltramo.conda\envs\objdecbase\lib\site-packages\absl\app.py", line 250, in _run_main
sys.exit(main(argv))
File "object_detection/model_main.py", line 105, in main
tf.estimator.train_and_evaluate(estimator, train_spec, eval_specs[0])
File "C:\Users\enrico.beltramo.conda\envs\objdecbase\lib\site-packages\tensorflow_estimator\python\estimator\training.py", line 473, in train_and_evaluate
return executor.run()
File "C:\Users\enrico.beltramo.conda\envs\objdecbase\lib\site-packages\tensorflow_estimator\python\estimator\training.py", line 613, in run
return self.run_local()
File "C:\Users\enrico.beltramo.conda\envs\objdecbase\lib\site-packages\tensorflow_estimator\python\estimator\training.py", line 714, in run_local
saving_listeners=saving_listeners)
File "C:\Users\enrico.beltramo.conda\envs\objdecbase\lib\site-packages\tensorflow_estimator\python\estimator\estimator.py", line 370, in train
loss = self._train_model(input_fn, hooks, saving_listeners)
File "C:\Users\enrico.beltramo.conda\envs\objdecbase\lib\site-packages\tensorflow_estimator\python\estimator\estimator.py", line 1161, in _train_model
return self._train_model_default(input_fn, hooks, saving_listeners)
File "C:\Users\enrico.beltramo.conda\envs\objdecbase\lib\site-packages\tensorflow_estimator\python\estimator\estimator.py", line 1191, in _train_model_default
features, labels, ModeKeys.TRAIN, self.config)
File "C:\Users\enrico.beltramo.conda\envs\objdecbase\lib\site-packages\tensorflow_estimator\python\estimator\estimator.py", line 1149, in _call_model_fn
model_fn_results = self._model_fn(features=features, **kwargs)
File "C:\Projects\CORAL\ObjectDetection\models-master\research\object_detection\model_lib.py", line 308, in model_fn
features[fields.InputDataFields.true_image_shape])
File "C:\Projects\CORAL\ObjectDetection\models-master\research\object_detection\meta_architectures\ssd_meta_arch.py", line 600, in predict
preprocessed_inputs)
File "C:\Projects\CORAL\ObjectDetection\models-master\research\object_detection\models\ssd_mobilenet_v1_ppn_feature_extractor.py", line 83, in extract_features
'image_features': image_features['Conv2d_11_pointwise']
File "C:\Projects\CORAL\ObjectDetection\models-master\research\object_detection\models\feature_map_generators.py", line 781, in pooling_pyramid_feature_maps
image_features = image_features[image_features.keys()[0]]
TypeError: 'dict_keys' object is not subscriptable

with other pretrained models (i.e mobile net v1), it works correctly