Keras DenseNet121 breaks on opencv dnn

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following http://answers.opencv.org/question/18... I'm trying to get densenet to work on openCV DNN but getting:

"error: OpenCV(3.4.2) /io/opencv/modules/dnn/src/tensorflow/tf_graph_simplifier.cpp:712: error: (-2:Unspecified error) Tensor's data type is not supported in function 'getTensorContent'"

import numpy as np
from keras import applications
from keras import backend as K
import cv2 as cv
import tensorflow as tf

model = applications.densenet.DenseNet121(input_shape=(224, 224, 3), weights='imagenet', include_top=True)
K.set_learning_phase(0)
sess = K.get_session()

print(model.input, model.outputs)

## Tensor("input_1:0", shape=(?, 224, 224, 3), dtype=float32) [<tf.Tensor 'fc1000/Softmax:0' shape=(?, 1000) dtype=float32>]

from tensorflow.python.tools import freeze_graph
from tensorflow.python.tools import optimize_for_inference_lib

MODEL_PATH = 'out'
MODEL_NAME = 'test'
input_node_name = 'input_1'
output_node_name = 'fc1000/Softmax'
!rm -rf {MODEL_PATH}/

tf.train.write_graph(sess.graph_def, MODEL_PATH, f'{MODEL_NAME}_graph.pb', as_text=False)
tf.train.write_graph(sess.graph_def, MODEL_PATH, f'{MODEL_NAME}_graph.pbtxt')
tf.train.Saver().save(sess, f'{MODEL_PATH}/{MODEL_NAME}.chkp')

freeze_graph.freeze_graph(f'{MODEL_PATH}/{MODEL_NAME}_graph.pbtxt',
                          None, False,
                          f'{MODEL_PATH}/{MODEL_NAME}.chkp',
                          output_node_name,
                          "save/restore_all",
                          "save/Const:0",
                          f'{MODEL_PATH}/frozen_{MODEL_NAME}.pb',
                          True, "")

graph_def = tf.GraphDef()
with tf.gfile.Open(f'{MODEL_PATH}/frozen_{MODEL_NAME}.pb', "rb") as f:
    graph_def.ParseFromString(f.read())

output_graph_def = optimize_for_inference_lib.optimize_for_inference(
    graph_def, [input_node_name], [output_node_name], tf.float32.as_datatype_enum)

with tf.gfile.GFile(f'{MODEL_PATH}/opt_{MODEL_NAME}.pb', "wb") as f:
    f.write(output_graph_def.SerializeToString())

# Strip Const nodes.
for i in reversed(range(len(graph_def.node))):
    if graph_def.node[i].op == 'Const':
        del graph_def.node[i]
#     for attr in ['T', 'data_format', 'Tshape', 'N', 'Tidx', 'Tdim',
#                  'use_cudnn_on_gpu', 'Index', 'Tperm', 'is_training',
#                  'Tpaddings']:
#         if attr in graph_def.node[i].attr:
#             del graph_def.node[i].attr[attr]

# Save stripped model.
tf.train.write_graph(graph_def, "", f'{MODEL_PATH}/stripped_{MODEL_NAME}.pbtxt', as_text=True)

net = cv.dnn.readNetFromTensorflow(f'{MODEL_PATH}/opt_{MODEL_NAME}.pb', f'{MODEL_PATH}/stripped_{MODEL_NAME}.pbtxt')

error: OpenCV(3.4.2) /io/opencv/modules/dnn/src/tensorflow/tf_graph_simplifier.cpp:712: error: (-2:Unspecified error) Tensor's data type is not supported in function 'getTensorContent'

It's hard to tell which node is causing that from the error. any idea please? cheers