System information (version)

OpenCV => 4.0.0
Operating System / Platform => Ubuntu 16.04 LTS
Compiler => cmake

Detailed description

When I use the newest version of tf_text_graph_ssd.py to generate graph txt file for my own tensorflow model, I keep getting this error:

Traceback (most recent call last):
  File "tf_text_graph_ssd.py", line 368, in <module>
    createSSDGraph(args.input, args.config, args.output)
  File "tf_text_graph_ssd.py", line 232, in createSSDGraph
    assert(graph_def.node[0].op == 'Placeholder')
AssertionError

Please take a look to the new version, I honestly don't know why it does not work while the other Issue post says it worked. Thank you!